Canvas2DLayerManager shouldn't use a task observer

sky/engine/platform/graphics/Canvas2DLayerManager.h

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 #ifndef Canvas2DLayerManager_h
 #define Canvas2DLayerManager_h
 
+#include "platform/Timer.h"
 #include "platform/graphics/Canvas2DLayerBridge.h"
-#include "public/platform/WebThread.h"
 
 class Canvas2DLayerManagerTest;
 
 namespace blink {
 
-class PLATFORM_EXPORT Canvas2DLayerManager : public WebThread::TaskObserver {
+class PLATFORM_EXPORT Canvas2DLayerManager {
 public:
     static Canvas2DLayerManager& get();
 
     void init(size_t maxBytesAllocated, size_t targetBytesAllocated);
     virtual ~Canvas2DLayerManager();
 
     void layerTransientResourceAllocationChanged(Canvas2DLayerBridge*, intptr_t deltaBytes = 0);
     void layerDidDraw(Canvas2DLayerBridge*);
 
     bool isInList(Canvas2DLayerBridge*) const;
 private:
     Canvas2DLayerManager();
 
     // internal methods
     void freeMemoryIfNecessary();
     void addLayerToList(Canvas2DLayerBridge*);
-    virtual void willProcessTask() OVERRIDE;
-    virtual void didProcessTask() OVERRIDE;
+
+    void limitPendingFramesTimerFired(Timer<Canvas2DLayerManager>*);
 
     size_t m_bytesAllocated;
     size_t m_maxBytesAllocated;
     size_t m_targetBytesAllocated;
-    bool m_taskObserverActive;
+    Timer<Canvas2DLayerManager> m_limitPendingFramesTimer;
     DoublyLinkedList<Canvas2DLayerBridge> m_layerList;
 
     friend class ::Canvas2DLayerManagerTest; // for unit testing
 };
 
 } // namespace blink
 
 #endif