Move overscroll bounce to impl thread

cc/input/scroll_elasticity_controller.h

Index: cc/input/scroll_elasticity_controller.h
diff --git a/cc/input/scroll_elasticity_controller.h b/cc/input/scroll_elasticity_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..382ae610a7d18f65c7223aa285789703c68c8684
--- /dev/null
+++ b/cc/input/scroll_elasticity_controller.h
@@ -0,0 +1,42 @@
+// 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_INPUT_SCROLL_ELASTICITY_CONTROLLER_H_
+#define CC_INPUT_SCROLL_ELASTICITY_CONTROLLER_H_
+
+#include "base/time/time.h"
+#include "cc/base/cc_export.h"
+#include "ui/gfx/geometry/vector2d_f.h"
+
+namespace cc {
+
+class CC_EXPORT ScrollElasticityController {
+ public:
+  virtual void WillShutdown() = 0;
+  virtual void Animate(base::TimeTicks time) = 0;
+};
+
+class CC_EXPORT ScrollElasticityControllerClient {
+ public:
+  virtual void BindToController(ScrollElasticityController* controller) = 0;
+
+  virtual bool allowsHorizontalStretching() const = 0;
+  virtual bool allowsVerticalStretching() const = 0;
+  virtual gfx::Vector2dF stretchAmount() const = 0;
+  virtual bool pinnedInDirection(const gfx::Vector2dF& delta) const = 0;
+  virtual bool canScrollHorizontally() const = 0;
+  virtual bool canScrollVertically() const = 0;
+  virtual gfx::Vector2dF absoluteScrollPosition() const = 0;
+
+  virtual void immediateScrollBy(const gfx::Vector2dF& delta) = 0;
+  virtual void immediateScrollByWithoutContentEdgeConstraints(const gfx::Vector2dF& delta) = 0;
+  virtual void startSnapRubberbandTimer() = 0;
+  virtual void stopSnapRubberbandTimer() = 0;
+
+  virtual void adjustScrollPositionToBoundsIfNecessary() = 0;
+};
+
+}  // namespace cc
+
+#endif  // CC_INPUT_SCROLL_ELASTICITY_CONTROLLER_H_