[SyncFS] Add verbose logging to RemoteToLocalSyncer

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

Review URL: https://codereview.chromium.org/108693003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240276 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240276