Correctly reset ScrollAnimator animation state after cancelling animation

third_party/WebKit/Source/platform/scroll/ScrollAnimator.cpp

 /*
  * Copyright (c) 2011, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 94 matching lines @@
 
     TRACE_EVENT0("blink", "ScrollAnimator::scroll");
 
     if (granularity == ScrollByPrecisePixel) {
         // Cancel scroll animation because asked to instant scroll.
         if (hasRunningAnimation())
             cancelAnimation();
         return ScrollAnimatorBase::userScroll(granularity, delta);
     }
 
+    bool needsPostAnimationCleanup = m_runState == RunState::PostAnimationCleanup;
+    if (m_runState == RunState::PostAnimationCleanup)
+        resetAnimationState();
+
     FloatSize consumedDelta = computeDeltaToConsume(delta);
 
     FloatPoint targetPos = desiredTargetPosition();
     targetPos.move(consumedDelta);
 
     if (willAnimateToOffset(targetPos)) {
         m_lastGranularity = granularity;
         // Report unused delta only if there is no animation running. See
         // comment below regarding scroll latching.
         // TODO(bokan): Need to standardize how ScrollAnimators report
         // unusedDelta. This differs from ScrollAnimatorMac currently.
         return ScrollResult(true, true, 0, 0);
     }
+
+    // If the run state when this method was called was PostAnimationCleanup and
+    // we're not starting an animation, stay in PostAnimationCleanup state so
+    // that the main thread scrolling reason can be removed.
+    if (needsPostAnimationCleanup)
+        m_runState = RunState::PostAnimationCleanup;
+
     // Report unused delta only if there is no animation and we are not
     // starting one. This ensures we latch for the duration of the
     // animation rather than animating multiple scrollers at the same time.
     return ScrollResult(false, false, delta.width(), delta.height());
 }
 
 bool ScrollAnimator::willAnimateToOffset(const FloatPoint& targetPos)
 {
     if (m_runState == RunState::PostAnimationCleanup)
         resetAnimationState();
@@ skipping 264 matching lines @@
     }
     return true;
 }
 
 DEFINE_TRACE(ScrollAnimator)
 {
     ScrollAnimatorBase::trace(visitor);
 }
 
 } // namespace blink