Bug 1507531 - FilePicker will request WRITE_EXTERNAL_STORAGE; r=JanH

"Prior to Android 8.0 (API level 26), if an app requested a permission at
runtime and the permission was granted, the system would also incorrectly
grant the app the rest of the permissions that belonged to the same permission
group, and that were registered in the manifest.

For apps targeting Android 8.0, this behavior has been corrected. The app is
granted only the permissions it has explicitly requested. However, once the
user grants a permission to the app, all subsequent requests for permissions
in that permission group are automatically granted."
https://developer.android.com/about/versions/oreo/android-8.0-changes#rmp

Our FilePicker can delegate other applications to record media files
(photo/audio/video) which are then to be sent to websites. They must be saved
locally before the upload, scenario that wasn't possible anymore on Oreo+
because of the change in how Android handles runtime permissions.

As a way to get around this one could grant the "Storage" permission from
System Settings which would grant the app both READ and WRITE access.
But for actually being prepared to handle all situations our FilePicker must
ask for the WRITE_EXTERNAL_STORAGE permission at runtime.

Differential Revision: https://phabricator.services.mozilla.com/D20821

--HG--
extra : moz-landing-system : lando

mobile/android/base/java/org/mozilla/gecko/FilePicker.java

@@ -114,13 +114,13 @@ public class FilePicker implements BundleEventListener {
 
     private static String[] getPermissionsForMimeType(final String mimeType) {
         if (mimeType.startsWith("audio/")) {
-            return new String[] { Manifest.permission.READ_EXTERNAL_STORAGE };
+            return new String[] { Manifest.permission.WRITE_EXTERNAL_STORAGE };
         } else if (mimeType.startsWith("image/")) {
-            return new String[] { Manifest.permission.CAMERA, Manifest.permission.READ_EXTERNAL_STORAGE };
+            return new String[] { Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE };
         } else if (mimeType.startsWith("video/")) {
-            return new String[] { Manifest.permission.CAMERA, Manifest.permission.READ_EXTERNAL_STORAGE };
+            return new String[] { Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE };
         }
-        return new String[] { Manifest.permission.CAMERA, Manifest.permission.READ_EXTERNAL_STORAGE };
+        return new String[] { Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE };
     }
 
     private static boolean hasPermissionsForMimeType(final String mimeType, final String[] availPermissions) {