[SyncFS] Misc fix and polish for SyncEngine and SyncEngineInitializer

 * Add retry limit to SyncEngineInitializer,
 * Rename drive_api and drive_api_service to drive_service for consistency,
 * Add missing DriveAPIService initialization,
 * Add RunSoon as a utility.

R=kinuko, nhiroki
BUG=240165
NOTRY=true

Review URL: https://codereview.chromium.org/25539002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226556 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226556
Fix the DCHECK when calling MediaSourcePlayer::SetVideoSurface()

SetVideoSurface() can happen when is previous call is waiting for decoder job to finish.
Don't add it to the pending queue if it is already there.

BUG=285950

Review URL: https://codereview.chromium.org/25432002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226557 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226557