cc: Allow the main thread to cancel commits

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index f04871aa42834f5798c61ce9716c104f9f51ed20..2ec3eacbc4dfe7734b039b38f232c4d2d610a491 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -165,6 +165,7 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
   const RendererCapabilities& GetRendererCapabilities() const;
 
   void SetNeedsAnimate();
+  virtual void SetNeedsUpdateLayers();
   virtual void SetNeedsCommit();
   virtual void SetNeedsFullTreeSync();
   void SetNeedsRedraw();
@@ -189,6 +190,7 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
   gfx::Size device_viewport_size() const { return device_viewport_size_; }
   float overdraw_bottom_height() const { return overdraw_bottom_height_; }
 
+  void ApplyPageScaleDeltaFromImplSide(float page_scale_delta);
   void SetPageScaleFactorAndLimits(float page_scale_factor,
                                    float min_page_scale_factor,
                                    float max_page_scale_factor);