First programmatic smooth scroll should run on the compositor if it can

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 261 matching lines @@
         m_compositorAnimationId = 0;
         m_compositorAnimationGroupId = 0;
         if (m_runState == RunState::WaitingToCancelOnCompositor) {
             postAnimationCleanupAndReset();
             return;
         }
     }
 
     if (m_runState == RunState::WaitingToSendToCompositor
         || m_runState == RunState::RunningOnCompositorButNeedsUpdate) {
+        if (!m_compositorAnimationAttachedToLayerId)
+            reattachCompositorPlayerIfNeeded(getScrollableArea()->compositorAnimationTimeline());
+
         if (m_runState == RunState::RunningOnCompositorButNeedsUpdate) {
             // Abort the running animation before a new one with an updated
             // target is added.
             abortAnimation();
 
             m_compositorAnimationId = 0;
             m_compositorAnimationGroupId = 0;
 
             m_animationCurve->updateTarget(m_timeFunction() - m_startTime,
                 compositorOffsetFromBlinkOffset(m_targetOffset));
@@ skipping 107 matching lines @@
     }
     return true;
 }
 
 DEFINE_TRACE(ScrollAnimator)
 {
     ScrollAnimatorBase::trace(visitor);
 }
 
 } // namespace blink