Better local discovery logging.

NOTRY=true

Review URL: https://codereview.chromium.org/25507004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226674 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226674
[SyncFS] Add SyncEngineContext

 * SyncEngineContext is an accessor to metadata_database and drive_service
   in SyncEngine from SyncTask.

R=kinuko, nhiroki
BUG=240165
NOTRY=true

Review URL: https://codereview.chromium.org/25701002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226675 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226675