CC AnimationHost: Fix ProgrammaticScrollAnimator detach scope.

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/scroll/ProgrammaticScrollAnimator.h"
 
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/IntPoint.h"
 #include "platform/graphics/GraphicsLayer.h"
@@ skipping 198 matching lines @@
 void ProgrammaticScrollAnimator::reattachCompositorPlayerIfNeeded(WebCompositorAnimationTimeline* timeline)
 {
     int compositorAnimationAttachedToLayerId = 0;
     if (m_scrollableArea->layerForScrolling())
         compositorAnimationAttachedToLayerId = m_scrollableArea->layerForScrolling()->platformLayer()->id();
 
     if (compositorAnimationAttachedToLayerId != m_compositorAnimationAttachedToLayerId) {
         if (m_compositorPlayer && timeline) {
             // Detach from old layer (if any).
             if (m_compositorAnimationAttachedToLayerId) {
-                ASSERT(m_compositorPlayer->isLayerAttached());
-                m_compositorPlayer->detachLayer();
+                if (m_compositorPlayer->isLayerAttached())
+                    m_compositorPlayer->detachLayer();
                 timeline->playerDestroyed(*this);
             }
             // Attach to new layer (if any).
             if (compositorAnimationAttachedToLayerId) {
                 ASSERT(m_scrollableArea->layerForScrolling());
+                ASSERT(!m_compositorPlayer->isLayerAttached());
                 timeline->playerAttached(*this);
                 m_compositorPlayer->attachLayer(m_scrollableArea->layerForScrolling()->platformLayer());
             }
             m_compositorAnimationAttachedToLayerId = compositorAnimationAttachedToLayerId;
         }
     }
 }
 
 void ProgrammaticScrollAnimator::layerForCompositedScrollingDidChange(WebCompositorAnimationTimeline* timeline)
 {
@@ skipping 43 matching lines @@
 {
     notifyCompositorAnimationFinished(group);
 }
 
 WebCompositorAnimationPlayer* ProgrammaticScrollAnimator::compositorPlayer() const
 {
     return m_compositorPlayer.get();
 }
 
 } // namespace blink