Update from https://crrev.com/308996

cc/input/scroll_elasticity_helper.h

 // 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_HELPER_H_
 #define CC_INPUT_SCROLL_ELASTICITY_HELPER_H_
 
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
 #include "ui/gfx/geometry/vector2d_f.h"
@@ skipping 28 matching lines @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  * THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // Interface between a LayerTreeHostImpl and the ScrollElasticityController. It
 // would be possible, in principle, for LayerTreeHostImpl to implement this
 // interface itself. This artificial boundary is introduced to reduce the amount
 // of logic and state held directly inside LayerTreeHostImpl.
 class CC_EXPORT ScrollElasticityHelper {
  public:
-  explicit ScrollElasticityHelper(LayerTreeHostImpl* layer_tree);
-  ~ScrollElasticityHelper();
+  static ScrollElasticityHelper* CreateForLayerTreeHostImpl(
+      LayerTreeHostImpl* layer_tree_host_impl);
 
-  bool AllowsHorizontalStretching();
-  bool AllowsVerticalStretching();
+  virtual ~ScrollElasticityHelper() {}
+
   // The amount that the view is stretched past the normal allowable bounds.
-  // The "overhang" amount.
-  gfx::Vector2dF StretchAmount();
-  bool PinnedInDirection(const gfx::Vector2dF& direction);
-  bool CanScrollHorizontally();
-  bool CanScrollVertically();
-
-  // Return the absolute scroll position, not relative to the scroll origin.
-  gfx::Vector2dF AbsoluteScrollPosition();
-
-  void ImmediateScrollBy(const gfx::Vector2dF& scroll);
-  void ImmediateScrollByWithoutContentEdgeConstraints(
-      const gfx::Vector2dF& scroll);
-  void StartSnapRubberbandTimer();
-  void StopSnapRubberbandTimer();
-  void SnapRubberbandTimerFired();
-
-  // If the current scroll position is within the overhang area, this function
-  // will cause
-  // the page to scroll to the nearest boundary point.
-  void AdjustScrollPositionToBoundsIfNecessary();
-
- private:
-  LayerTreeHostImpl* layer_tree_host_impl_;
-  gfx::Vector2dF stretch_offset_;
-  bool timer_active_;
+  virtual gfx::Vector2dF StretchAmount() = 0;
+  virtual void SetStretchAmount(const gfx::Vector2dF& stretch_amount) = 0;
+  // Returns true if either component of |direction| is pointing in a direction
+  // in which it is not possible to scroll any farther. It is only in this
+  // circumstance that an overscroll in that direction may begin.
+  // TODO(ccameron): Note that it is possible for a scroll to occur against a
+  // previous over-scroll. Such a scroll needs to first cancel out the
+  // over-scroll, and only then may it start scrolling away from the edge.
+  virtual bool PinnedInDirection(const gfx::Vector2dF& direction) = 0;
+  // Whether or not the content of the page is scrollable in each direction.
+  virtual bool CanScrollHorizontally() = 0;
+  virtual bool CanScrollVertically() = 0;
+  // Request that the controller have its Animate method called for the next
+  // frame.
+  virtual void RequestAnimate() = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLL_ELASTICITY_HELPER_H_