Use input events to improve vsync scheduling

cc/layer_tree_host_impl.h

Index: cc/layer_tree_host_impl.h
diff --git a/cc/layer_tree_host_impl.h b/cc/layer_tree_host_impl.h
index 97531626a31368caa14ece6ce2cab51c3e33ae51..9ca34203beff4055ecc6e18b90606c54a098f0a9 100644
--- a/cc/layer_tree_host_impl.h
+++ b/cc/layer_tree_host_impl.h
@@ -45,6 +45,7 @@ public:
     virtual void onSwapBuffersCompleteOnImplThread() = 0;
     virtual void onVSyncParametersChanged(base::TimeTicks timebase, base::TimeDelta interval) = 0;
     virtual void didVSync(base::TimeTicks frameTime) = 0;
+    virtual void didReceiveLastInputEventForVSync() = 0;
     virtual void onCanDrawStateChanged(bool canDraw) = 0;
     virtual void onHasPendingTreeStateChanged(bool hasPendingTree) = 0;
     virtual void setNeedsRedrawOnImplThread() = 0;
@@ -77,6 +78,7 @@ public:
     virtual void startPageScaleAnimation(gfx::Vector2d targetOffset, bool anchorPoint, float pageScale, base::TimeTicks startTime, base::TimeDelta duration) OVERRIDE;
     virtual void scheduleAnimation() OVERRIDE;
     virtual bool haveTouchEventHandlersAt(const gfx::Point&) OVERRIDE;
+    virtual void didReceiveLastInputEventForVSync() OVERRIDE;
 
     struct CC_EXPORT FrameData : public RenderPassSink {
         FrameData();