sync: don't run session sync SyncStartFlare for unsynced tabs

BUG=80194

Review URL: https://codereview.chromium.org/145353009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249221 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249221
Blink roll 166433:166492

TBR=pilgrim@chromium.org

Review URL: https://codereview.chromium.org/144003021

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249222 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249223 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249223