[Android] Report the correct scroll gesture start time

The scroll start time should be the time at which initial scroll movement
occurred, not the time when the initial scroll anchor was pressed. Report
the former from ContentViewGestureHandler.

BUG=311402

Review URL: https://codereview.chromium.org/42233003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231198 0039d316-1c4b-4281-b951-d872f2087c98
Fix settings overlay "shifting" when shown.

aboxhall@s r228479 simplified |setOverlayVisible_| but I need to re-complicate
it as |onVisibilityChanged_| must be called before |fadeCompleted_| to ensure
the right sizes of frozen pages are calculated/set before transitions end.

R=aboxhall@chromium.org
BUG=307388
TEST=OptionsWebUINavigationTest.OverlayShowDoesntShift, visual (see bug)

Review URL: https://codereview.chromium.org/42393002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231199 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231199