The problem is in the onActivityResult() method for KitKat which returns the URI. You need to get the realpath of the imagefile.
Notice how i get the Real Path of the IMG by calling :
KitkatPath = Uri.parse("file://"+getPath(MobilestyxAppActivity.this, result)); in the onActivityResult().
You must add the string "file://" for it to work.
PS : I have gathered the code from various sources and modified it.
Look at my code below which works for Kitkat & Lolipop and other low versions of Android.
/** CODE FOR FILE UPLOAD*/  
private static final int INPUT_FILE_REQUEST_CODE = 1;
private static final int FILECHOOSER_RESULTCODE = 1;
private ValueCallback<Uri> mUploadMessage;
private Uri mCapturedImageURI = null;
private ValueCallback<Uri[]> mFilePathCallback;
private String mCameraPhotoPath;
Uri KitkatPath ;   
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        if (requestCode != INPUT_FILE_REQUEST_CODE || mFilePathCallback == null) {
            super.onActivityResult(requestCode, resultCode, data);
            return;
        }
        Uri[] results = null;
        // Check that the response is a good one
        if (resultCode == Activity.RESULT_OK) {
            if (data == null) {
                // If there is not data, then we may have taken a photo
                if (mCameraPhotoPath != null) {
                    results = new Uri[]{Uri.parse(mCameraPhotoPath)};
                }
            } else {
                String dataString = data.getDataString();
                if (dataString != null) {
                    results = new Uri[]{Uri.parse(dataString)};
                }
            }
        }
        mFilePathCallback.onReceiveValue(results);
        mFilePathCallback = null;
    } 
    else if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT) {
        System.out.println("In KitKat Condition");
        if (requestCode != FILECHOOSER_RESULTCODE || mUploadMessage == null) {
            System.out.println("In != Null");
            super.onActivityResult(requestCode, resultCode, data);
            return;
        }
        if (requestCode == FILECHOOSER_RESULTCODE) {
            System.out.println("requestCode == FileChooser ResultCode");
            if (null == this.mUploadMessage) {
                System.out.println("In null == this.mUploadMessage");
                return;
            }
            Uri result = null;
            try {
                if (resultCode != RESULT_OK) {
                    result = null;
                } else {
                    //newcode
                    // retrieve from the private variable if the intent is null
                    result = data == null ? mCapturedImageURI : data.getData();
                    KitkatPath = Uri.parse("file://"+getPath(MobilestyxAppActivity.this, result));
                    System.out.println("KitkatPath== "+KitkatPath);
                    System.out.println("result = "+result);
                }
            } catch (Exception e) {
               // Toast.makeText(getApplicationContext(), "activity :" + e,                            Toast.LENGTH_LONG).show();
                e.printStackTrace();
            }
           // mUploadMessage.onReceiveValue(result);
            mUploadMessage.onReceiveValue(KitkatPath);
            System.out.println("mUploadMessage = "+mUploadMessage);
            mUploadMessage = null;
        }
    }
    return;
}
 /** CODE FOR FILE UPLOAD*/ 
public static String getPath(final Context context, final Uri uri) {
    final boolean isKitKat = Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT;
    // DocumentProvider
    if (isKitKat && DocumentsContract.isDocumentUri(context, uri)) {
        // ExternalStorageProvider
        if (isExternalStorageDocument(uri)) {
            final String docId = DocumentsContract.getDocumentId(uri);
            final String[] split = docId.split(":");
            final String type = split[0];
            if ("primary".equalsIgnoreCase(type)) {
                return Environment.getExternalStorageDirectory() + "/" + split[1];
            }
            // TODO handle non-primary volumes
        }
        // DownloadsProvider
        else if (isDownloadsDocument(uri)) {
            final String id = DocumentsContract.getDocumentId(uri);
            final Uri contentUri = ContentUris.withAppendedId(
                    Uri.parse("content://downloads/public_downloads"), Long.valueOf(id));
            return getDataColumn(context, contentUri, null, null);
        }
        // MediaProvider
        else if (isMediaDocument(uri)) {
            final String docId = DocumentsContract.getDocumentId(uri);
            final String[] split = docId.split(":");
            final String type = split[0];
            Uri contentUri = null;
            if ("image".equals(type)) {
                contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
            } else if ("video".equals(type)) {
                contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
            } else if ("audio".equals(type)) {
                contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
            }
            final String selection = "_id=?";
            final String[] selectionArgs = new String[] {
                    split[1]
            };
            return getDataColumn(context, contentUri, selection, selectionArgs);
        }
    }
    // MediaStore (and general)
    else if ("content".equalsIgnoreCase(uri.getScheme())) {
        // Return the remote address
        if (isGooglePhotosUri(uri))
            return uri.getLastPathSegment();
        return getDataColumn(context, uri, null, null);
    }
    // File
    else if ("file".equalsIgnoreCase(uri.getScheme())) {
        return uri.getPath();
    }
    return null;
}
/**
 * Get the value of the data column for this Uri. This is useful for
 * MediaStore Uris, and other file-based ContentProviders.
 *
 * @param context The context.
 * @param uri The Uri to query.
 * @param selection (Optional) Filter used in the query.
 * @param selectionArgs (Optional) Selection arguments used in the query.
 * @return The value of the _data column, which is typically a file path.
 */
public static String getDataColumn(Context context, Uri uri, String selection,
        String[] selectionArgs) {
    Cursor cursor = null;
    final String column = "_data";
    final String[] projection = {
            column
    };
    try {
        cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs,
                null);
        if (cursor != null && cursor.moveToFirst()) {
            final int index = cursor.getColumnIndexOrThrow(column);
            return cursor.getString(index);
        }
    } finally {
        if (cursor != null)
            cursor.close();
    }
    return null;
}
/**
 * @param uri The Uri to check.
 * @return Whether the Uri authority is ExternalStorageProvider.
 */
public static boolean isExternalStorageDocument(Uri uri) {
    return "com.android.externalstorage.documents".equals(uri.getAuthority());
}
/**
 * @param uri The Uri to check.
 * @return Whether the Uri authority is DownloadsProvider.
 */
public static boolean isDownloadsDocument(Uri uri) {
    return "com.android.providers.downloads.documents".equals(uri.getAuthority());
}
/**
 * @param uri The Uri to check.
 * @return Whether the Uri authority is MediaProvider.
 */
public static boolean isMediaDocument(Uri uri) {
    return "com.android.providers.media.documents".equals(uri.getAuthority());
}
/**
 * @param uri The Uri to check.
 * @return Whether the Uri authority is Google Photos.
 */
public static boolean isGooglePhotosUri(Uri uri) {
    return "com.google.android.apps.photos.content".equals(uri.getAuthority());
}
private File createImageFile() throws IOException {
    // Create an image file name
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date(heightDiff));
    String imageFileName = "JPEG_" + timeStamp + "_";
    File storageDir = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File imageFile = File.createTempFile(
            imageFileName,  /* prefix */
            ".jpg",         /* suffix */
            storageDir      /* directory */
    );
    return imageFile;
}
& now in the WebViewChromeClient ---
browser.setWebChromeClient(new WebChromeClient()
                {
                // For Android 5.0
                public boolean onShowFileChooser(WebView view, ValueCallback<Uri[]> filePath, WebChromeClient.FileChooserParams fileChooserParams) {
                    System.out.println("in 5.0");
                    // Double check that we don't have any existing callbacks
                    if (mFilePathCallback != null) {
                        mFilePathCallback.onReceiveValue(null);
                    }
                    mFilePathCallback = filePath;
                    Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                    if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
                        // Create the File where the photo should go
                        File photoFile = null;
                        try {
                            photoFile = createImageFile();
                            takePictureIntent.putExtra("PhotoPath", mCameraPhotoPath);
                        } catch (IOException ex) {
                            // Error occurred while creating the File
                          //  Log.e(TAG, "Unable to create Image File", ex);
                        }
                        // Continue only if the File was successfully created
                        if (photoFile != null) {
                            mCameraPhotoPath = "file:" + photoFile.getAbsolutePath();
                            takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT,
                                    Uri.fromFile(photoFile));
                        } else {
                            takePictureIntent = null;
                        }
                    }
                    Intent contentSelectionIntent = new Intent(Intent.ACTION_GET_CONTENT);
                    contentSelectionIntent.addCategory(Intent.CATEGORY_OPENABLE);
                    contentSelectionIntent.setType("image/*");
                    Intent[] intentArray;
                    if (takePictureIntent != null) {
                        intentArray = new Intent[]{takePictureIntent};
                    } else {
                        intentArray = new Intent[0];
                    }
                    Intent chooserIntent = new Intent(Intent.ACTION_CHOOSER);
                    chooserIntent.putExtra(Intent.EXTRA_INTENT, contentSelectionIntent);
                    chooserIntent.putExtra(Intent.EXTRA_TITLE, "Image Chooser");
                    chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS, intentArray);
                    startActivityForResult(chooserIntent, INPUT_FILE_REQUEST_CODE);
                    return true;
                }
                // openFileChooser for Android 3.0+
                public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType) {
                    System.out.println("in 3.0+");
                    mUploadMessage = uploadMsg;
                    // Create AndroidExampleFolder at sdcard
                    // Create AndroidExampleFolder at sdcard
                    File imageStorageDir = new File(
                            Environment.getExternalStoragePublicDirectory(
                                    Environment.DIRECTORY_PICTURES)
                            , "AndroidExampleFolder");
                    if (!imageStorageDir.exists()) {
                        // Create AndroidExampleFolder at sdcard
                        imageStorageDir.mkdirs();
                    }
                    // Create camera captured image file path and name
                    File file = new File(
                            imageStorageDir + File.separator + "IMG_"
                                    + String.valueOf(System.currentTimeMillis())
                                    + ".jpg");
                    mCapturedImageURI = Uri.fromFile(file);
                    //
                    // Camera capture image intent
                    final Intent captureIntent = new Intent(
                            android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
                    captureIntent.putExtra(MediaStore.EXTRA_OUTPUT, mCapturedImageURI);
                    Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                    i.addCategory(Intent.CATEGORY_OPENABLE);
                    i.setType("image/*");
                    // Create file chooser intent
                    Intent chooserIntent = Intent.createChooser(i, "Image Chooser");
                    // Set camera intent to file chooser
                    chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS
                            , new Parcelable[] { captureIntent });
                    // On select image call onActivityResult method of activity
                    startActivityForResult(chooserIntent, FILECHOOSER_RESULTCODE);
                }
                // openFileChooser for Android < 3.0
                public void openFileChooser(ValueCallback<Uri> uploadMsg) {
                    System.out.println("in <3.0");
                    openFileChooser(uploadMsg, "");
                }
                // openFileChooser for other Android versions
                public void openFileChooser(ValueCallback<Uri> uploadMsg,
                        String acceptType, String capture) {
                    System.out.println("in OTHER");
                    openFileChooser(uploadMsg, acceptType);
                }