DevTools: add instrumentation for deferred canvas rasterization

Source/core/inspector/InspectorTimelineAgent.h

Index: Source/core/inspector/InspectorTimelineAgent.h
diff --git a/Source/core/inspector/InspectorTimelineAgent.h b/Source/core/inspector/InspectorTimelineAgent.h
index b58915660d617ba7e036a9b0966a78f52502de3b..38ee5a6d2f060cb5e45e775c3f8b00e933d1da5e 100644
--- a/Source/core/inspector/InspectorTimelineAgent.h
+++ b/Source/core/inspector/InspectorTimelineAgent.h
@@ -121,6 +121,8 @@ public:
     virtual void start(ErrorString*, const int* maxCallStackDepth, const bool* includeDomCounters, const bool* includeNativeMemoryStatistics);
     virtual void stop(ErrorString*);
 
+    void setLayerTreeId(int layerTreeId) { m_layerTreeId = layerTreeId; }
+    int layerTreeId() const { return m_layerTreeId; }
     int id() const { return m_id; }
 
     void didCommitLoad();
@@ -285,6 +287,7 @@ private:
     WeakPtrFactory<InspectorTimelineAgent> m_weakFactory;
     RefPtr<TimelineTraceEventProcessor> m_traceEventProcessor;
     unsigned m_styleRecalcElementCounter;
+    unsigned long long m_layerTreeId;
 };
 
 } // namespace WebCore