[SyncFS] Insert DVLOGs to for debugging

 * Insert DVLOGs for debugging
 * Drop unused parameter for demoted dirty tracker.
 * Add FileTracker accessor by parent tracker
 * Handle title change on MetadataDatabaseIndex


BUG=344769

Review URL: https://codereview.chromium.org/187203004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255012 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255012