[Android] Avoid early fling termination if initial time is non-positive

[Android] Avoid early fling termination if initial time is non-positive

Main thread animations provide no guarantees that the initial fling timestamp
will be strictly positive.  Consequently, a (valid) timestamp of 0 applied to
Android's fling animation curve will yield a zero-sized scroll delta.  Feeding
this scroll delta through WebViewImpl reports that scrolling is impossible, in
which case the fling will early terminate.  Avoid this case by early returning
on non-positive fling timestamps, aligning with Aura's fling behavior.

BUG=371854
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269594

[jdduke (slow), 2014-05-09 15:43:48]

bokan@: PTAL.  At some point I'd like to add a few smoke tests for
FlingAnimatorImplAndroid (we have coverage of the underyling Scroller class, and
unit tests were difficult previously because Scroller was a Java entity).  In
any case, this change is precisely what we do currently with Aura's
TouchFlingGestureCurve.

[bokan, 2014-05-09 15:50:22]

On 2014/05/09 15:43:48, jdduke wrote:
> bokan@: PTAL.  At some point I'd like to add a few smoke tests for
> FlingAnimatorImplAndroid (we have coverage of the underyling Scroller class,
and
> unit tests were difficult previously because Scroller was a Java entity).  In
> any case, this change is precisely what we do currently with Aura's
> TouchFlingGestureCurve.

Yup, LGTM

[jdduke (slow), 2014-05-09 15:51:37]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2014-05-09 15:53:38]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jdduke@chromium.org/275113002/1

[commit-bot: I haz the power, 2014-05-10 18:24:22]

Change committed as 269594