[Retry][SyncFS] Add verbose logging to SyncEngineInitializer and ListChangesTask

BUG=240165
R=kinuko@chromium.org, nhiroki@chromium.org

Review URL: https://codereview.chromium.org/104873015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241237 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241237
Disable AVFoundation by default

This is essentially a revert of r239758, where AVFoundation was enabled by
default on Macs. AVFoundation is causing browser crashes on every call
to getUserMedia on certain Macs, hence we are changing the switch from a
Disable switch to an Enable switch. 

BUG=288562,327532,329001
NOTRY=true

Review URL: https://codereview.chromium.org/116673002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241238 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241238