Revert of Revert of Early terminate flings when scrolling impossible (https://codereview.chromium.org/213743004/)

Reason for revert:
The broken fling layout test has been fixed in: https://codereview.chromium.org/219243010/

Original issue's description:
> Revert of Early terminate flings when scrolling impossible (https://codereview.chromium.org/136173004/)
> 
> Reason for revert:
> Broke a layout test, fast/events/touch/gesture/pad-gesture-fling.html
> 
> http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=fast%2Fevents%2Ftouch%2Fgesture%2Fpad-gesture-fling.html
> 
> 
> Original issue's description:
> > 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/
> > 
> > Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=260631
> 
> TBR=aelias@chromium.org,jochen@chromium.org,jdduke@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=260773

TBR=aelias@chromium.org,jochen@chromium.org,tkent@chromium.org

NOTRY=true

Review URL: https://codereview.chromium.org/222353002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@261187 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 27 insertions, 0 deletions

diff --git a/ui/gfx/android/scroller.cc b/ui/gfx/android/scroller.cc
index 96658b2..4a44741 100644
--- a/ui/gfx/android/scroller.cc
+++ b/ui/gfx/android/scroller.cc
@@ -276,6 +276,9 @@ bool Scroller::ComputeScrollOffset(base::TimeTicks time) {
   if (finished_)
     return false;
 
+  if (time == curr_time_)
+    return true;
+
   base::TimeDelta time_passed = time - start_time_;
 
   if (time_passed < base::TimeDelta()) {
diff --git a/ui/gfx/android/scroller_unittest.cc b/ui/gfx/android/scroller_unittest.cc
index af3c67a..9b1018d 100644
--- a/ui/gfx/android/scroller_unittest.cc
+++ b/ui/gfx/android/scroller_unittest.cc
@@ -63,6 +63,18 @@ TEST_F(ScrollerTest, Scroll) {
   EXPECT_GT(0.f, scroller.GetCurrVelocityY() * kDefaultDeltaY);
   EXPECT_TRUE(scroller.IsScrollingInDirection(kDefaultDeltaX, kDefaultDeltaY));
 
+  // Repeated offset computations at the same timestamp should yield identical
+  // results.
+  float curr_x = scroller.GetCurrX();
+  float curr_y = scroller.GetCurrY();
+  float curr_velocity_x = scroller.GetCurrVelocityX();
+  float curr_velocity_y = scroller.GetCurrVelocityY();
+  scroller.ComputeScrollOffset(start_time + scroll_duration / 2);
+  EXPECT_EQ(curr_x, scroller.GetCurrX());
+  EXPECT_EQ(curr_y, scroller.GetCurrY());
+  EXPECT_EQ(curr_velocity_x, scroller.GetCurrVelocityX());
+  EXPECT_EQ(curr_velocity_y, scroller.GetCurrVelocityY());
+
   // Advance to the end.
   scroller.ComputeScrollOffset(start_time + scroll_duration);
   EXPECT_EQ(scroller.GetFinalX(), scroller.GetCurrX());
@@ -123,6 +135,18 @@ TEST_F(ScrollerTest, Fling) {
   EXPECT_TRUE(
       scroller.IsScrollingInDirection(kDefaultVelocityX, kDefaultVelocityY));
 
+  // Repeated offset computations at the same timestamp should yield identical
+  // results.
+  float curr_x = scroller.GetCurrX();
+  float curr_y = scroller.GetCurrY();
+  float curr_velocity_x = scroller.GetCurrVelocityX();
+  float curr_velocity_y = scroller.GetCurrVelocityY();
+  scroller.ComputeScrollOffset(start_time + scroll_duration / 2);
+  EXPECT_EQ(curr_x, scroller.GetCurrX());
+  EXPECT_EQ(curr_y, scroller.GetCurrY());
+  EXPECT_EQ(curr_velocity_x, scroller.GetCurrVelocityX());
+  EXPECT_EQ(curr_velocity_y, scroller.GetCurrVelocityY());
+
   // Advance to the end.
   scroller.ComputeScrollOffset(start_time + scroll_duration);
   EXPECT_EQ(scroller.GetFinalX(), scroller.GetCurrX());