Early terminate flings when scrolling impossible
Previously, flings were terminated early only if the root layer overscrolled.
Now, flings will terminate if the fling target's |scrollBy()| method returns
false, providing consistency between layer types and saving battery on
sites with scrolling sublayers.
Also move |DidOverscrollParams| into content/ in anticipation of using it
directly in the overscroll IPC message.
Corresponding Blink patch:
https://codereview.chromium.org/
139493003/
Review URL: https://codereview.chromium.org/
136173004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@260631 0039d316-1c4b-4281-b951-d872f2087c98