Move overscroll bounce to impl thread

cc/trees/tree_scroll_elasticity_client.h

Index: cc/trees/tree_scroll_elasticity_client.h
diff --git a/cc/trees/tree_scroll_elasticity_client.h b/cc/trees/tree_scroll_elasticity_client.h
new file mode 100644
index 0000000000000000000000000000000000000000..3b5931741433b3f9055bc518de899fe011992403
--- /dev/null
+++ b/cc/trees/tree_scroll_elasticity_client.h
@@ -0,0 +1,46 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_TREES_TREE_SCROLL_ELASTICITY_CLIENT_H_
+#define CC_TREES_TREE_SCROLL_ELASTICITY_CLIENT_H_
+
+#include "cc/input/scroll_elasticity_controller.h"
+
+namespace cc {
+
+class LayerTreeHostImpl;
+
+class TreeScrollElasticityClient
+    : public ScrollElasticityControllerClient {
+ public:
+  TreeScrollElasticityClient(LayerTreeHostImpl* tree);
+  virtual ~TreeScrollElasticityClient();
+
+  ScrollElasticityController* controller() const { return controller_; }
+
+  // cc::ScrollElasticityControllerClient implementation:
+  void BindToController(ScrollElasticityController* controller) override;
+  bool allowsHorizontalStretching() const override;
+  bool allowsVerticalStretching() const override;
+  gfx::Vector2dF stretchAmount() const override;
+  bool pinnedInDirection(const gfx::Vector2dF& delta) const override;
+  bool canScrollHorizontally() const override;
+  bool canScrollVertically() const override;
+  gfx::Vector2dF absoluteScrollPosition() const override;
+  void immediateScrollBy(const gfx::Vector2dF& delta) override;
+  void immediateScrollByWithoutContentEdgeConstraints(const gfx::Vector2dF& delta) override;
+  void startSnapRubberbandTimer() override;
+  void stopSnapRubberbandTimer() override;
+  void adjustScrollPositionToBoundsIfNecessary() override;
+
+ private:
+  LayerTreeHostImpl* tree_;
+  gfx::Vector2dF stretch_offset_;
+  bool timer_active_;
+  ScrollElasticityController* controller_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_TREE_SCROLL_ELASTICITY_CLIENT_H_