[SyncFS] Implement non-conflict local folder addition.

 * Handles local folder addition to existing remote file.
 * Add MarkTrackerDirty to MetadataDatabase.
 * Reorder GetRegisteredAppIDs

BUG=240165

Review URL: https://codereview.chromium.org/77913002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236243 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236243