[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

Review URL: https://codereview.chromium.org/275113002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269594 0039d316-1c4b-4281-b951-d872f2087c98

content/child/fling_animator_impl_android.cc

@@ -66,6 +66,11 @@ void FlingAnimatorImpl::CancelFling() {
 
 bool FlingAnimatorImpl::apply(double time,
                               blink::WebGestureCurveTarget* target) {
+  // If the fling has yet to start, simply return and report true to prevent
+  // fling termination.
+  if (time <= 0)
+    return true;
+
   const base::TimeTicks time_ticks =
       base::TimeTicks() + base::TimeDelta::FromMicroseconds(
                               time * base::Time::kMicrosecondsPerSecond);