Fix scroll animation UpdateTarget for zero-duration segments

cc/animation/scroll_offset_animation_curve.cc

Index: cc/animation/scroll_offset_animation_curve.cc
diff --git a/cc/animation/scroll_offset_animation_curve.cc b/cc/animation/scroll_offset_animation_curve.cc
index a3831432897b6f8b3b71295254768597d06f2e8e..16ff073655ca669e4c4f750dcea192c685871f51 100644
--- a/cc/animation/scroll_offset_animation_curve.cc
+++ b/cc/animation/scroll_offset_animation_curve.cc
@@ -228,6 +228,15 @@ void ScrollOffsetAnimationCurve::UpdateTarget(
   gfx::Vector2dF old_delta = target_value_.DeltaFrom(initial_value_);
   gfx::Vector2dF new_delta = new_target.DeltaFrom(current_position);
 
+  // The last segement was of zero duration.
+  if ((total_animation_duration_ - last_retarget_).is_zero()) {
+    DCHECK_EQ(t, last_retarget_.InSecondsF());
+    total_animation_duration_ =
+        SegmentDuration(new_delta, duration_behavior_, base::TimeDelta());

[skobes, 2016/09/12 22:45:46]

Pass delayed_by here?

[ymalik, 2016/09/12 23:35:05]

Done.

+    target_value_ = new_target;
+    return;
+  }
+
   double old_duration =
       (total_animation_duration_ - last_retarget_).InSecondsF();
   double old_normalized_velocity = timing_function_->Velocity(