[Android] Suppress spurious overscroll releases from ScrollEnd gestures

The sensitivity of certain touchscreens may cause multiple ScrollBegin/ScrollEnd
gestures to be sent in what is a seemingly continous touch scroll.  Stop
releasing the overscroll glow in these cases; the effect's natural fade decay is
sufficient to end the effect.

NOTRY=true

Review URL: https://codereview.chromium.org/26925004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228736 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228736