Update from https://crrev.com/307330

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index d16234bad35b2e4badb5c6b6c2f73dfd04952693..46b8312ba820e59c5dac8574eabed66c9d67898f 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -50,14 +50,16 @@ struct RendererCapabilities;
 struct SelectionHandle;
 
 typedef std::list<UIResourceRequest> UIResourceRequestQueue;
+typedef SyncedProperty<AdditionGroup<gfx::Vector2dF>> SyncedElasticOverscroll;
 
 class CC_EXPORT LayerTreeImpl {
  public:
   static scoped_ptr<LayerTreeImpl> create(
       LayerTreeHostImpl* layer_tree_host_impl,
-      scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor) {
-    return make_scoped_ptr(
-        new LayerTreeImpl(layer_tree_host_impl, page_scale_factor));
+      scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
+      scoped_refptr<SyncedElasticOverscroll> elastic_overscroll) {
+    return make_scoped_ptr(new LayerTreeImpl(
+        layer_tree_host_impl, page_scale_factor, elastic_overscroll));
   }
   virtual ~LayerTreeImpl();
 
@@ -179,6 +181,13 @@ class CC_EXPORT LayerTreeImpl {
   SyncedProperty<ScaleGroup>* page_scale_factor();
   const SyncedProperty<ScaleGroup>* page_scale_factor() const;
 
+  SyncedElasticOverscroll* elastic_overscroll() {
+    return elastic_overscroll_.get();
+  }
+  const SyncedElasticOverscroll* elastic_overscroll() const {
+    return elastic_overscroll_.get();
+  }
+
   // Updates draw properties and render surface layer list, as well as tile
   // priorities. Returns false if it was unable to update.
   bool UpdateDrawProperties();
@@ -325,7 +334,8 @@ class CC_EXPORT LayerTreeImpl {
  protected:
   explicit LayerTreeImpl(
       LayerTreeHostImpl* layer_tree_host_impl,
-      scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor);
+      scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
+      scoped_refptr<SyncedElasticOverscroll> elastic_overscroll);
   void ReleaseResourcesRecursive(LayerImpl* current);
   float ClampPageScaleFactorToLimits(float page_scale_factor) const;
   void PushPageScaleFactorAndLimits(const float* page_scale_factor,
@@ -360,6 +370,8 @@ class CC_EXPORT LayerTreeImpl {
   float min_page_scale_factor_;
   float max_page_scale_factor_;
 
+  scoped_refptr<SyncedElasticOverscroll> elastic_overscroll_;
+
   typedef base::hash_map<int, LayerImpl*> LayerIdMap;
   LayerIdMap layer_id_map_;