Update from https://crrev.com/304121

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"
+
+namespace cc {
+
+class LayerTreeHostImpl;
+
+// ScrollElasticityHelper is based on
+// WebKit/Source/platform/mac/ScrollElasticityController.h
+/*
+ * Copyright (C) 2011 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * 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();
+
+  bool AllowsHorizontalStretching();
+  bool AllowsVerticalStretching();
+  // 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_;
+};
+
+}  // namespace cc
+
+#endif  // CC_INPUT_SCROLL_ELASTICITY_HELPER_H_