Move scroll event handlers from layer to layer tree view.

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 db7247a7415a1d724ef4543272d276ff4f5f5f4e..7ccb9f2ac3980c33d452ed7e045cc1803c296dec 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -207,6 +207,11 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
 
   void RegisterSelection(const LayerSelection& selection);
 
+  bool have_scroll_event_handlers() const {
+    return have_scroll_event_handlers_;
+  }
+  void SetHaveScrollEventHandlers(bool have_event_handlers);
+
   bool have_wheel_event_handlers() const { return have_wheel_event_handlers_; }
   void SetHaveWheelEventHandlers(bool have_event_handlers);
 
@@ -506,6 +511,7 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   SkColor background_color_;
   bool has_transparent_background_;
 
+  bool have_scroll_event_handlers_;
   bool have_wheel_event_handlers_;
 
   scoped_ptr<AnimationRegistrar> animation_registrar_;