Restore handling of new scroll when waiting to cancel current scroll on cc

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 129 matching lines @@
     // 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();
 
-    if (m_animationCurve && m_runState != RunState::WaitingToCancelOnCompositor) {
+    if (m_runState == RunState::WaitingToCancelOnCompositor) {
+        // Ignore user scroll if WaitingToCancelOnCompositor. Can be in this
+        // state when holding down an arrow.
+        // TODO(ymalik): Handle this case by either updating the target on the
+        // current scroll or starting a new animation (see crbug.com/599876).
+        return true;
+    }
+
+    if (m_animationCurve) {
         if ((targetPos - m_targetOffset).isZero())
             return true;
 
         m_targetOffset = targetPos;
         ASSERT(m_runState == RunState::RunningOnMainThread
             || m_runState == RunState::RunningOnCompositor
             || m_runState == RunState::RunningOnCompositorButNeedsUpdate
             || m_runState == RunState::RunningOnCompositorButNeedsTakeover);
 
         // Running on the main thread, simply update the target offset instead
@@ skipping 252 matching lines @@
     }
     return true;
 }
 
 DEFINE_TRACE(ScrollAnimator)
 {
     ScrollAnimatorBase::trace(visitor);
 }
 
 } // namespace blink