Route Scroll events through a cc::InputHandler

ui/compositor/overscroll/ui_scroll_input_manager.h

Index: ui/compositor/overscroll/ui_scroll_input_manager.h
diff --git a/ui/compositor/overscroll/ui_scroll_input_manager.h b/ui/compositor/overscroll/ui_scroll_input_manager.h
new file mode 100644
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+++ b/ui/compositor/overscroll/ui_scroll_input_manager.h
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+// Copyright 2016 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 UI_COMPOSITOR_OVERSCROLL_UI_SCROLL_INPUT_MANAGER_H_
+#define UI_COMPOSITOR_OVERSCROLL_UI_SCROLL_INPUT_MANAGER_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "cc/trees/element_id.h"
+#include "ui/compositor/compositor_export.h"
+
+namespace cc {
+class InputHandler;
+}
+
+namespace ui {
+
+class Layer;
+class ScrollEvent;
+class UIInputHandler;
+
+// UI-Thread helper for directing scroll events to the Compositor to enable
+// accelerated scrolling, and elastic scrolling on Mac.
+class COMPOSITOR_EXPORT UIScrollInputManager {
+ public:
+  explicit UIScrollInputManager(
+      const base::WeakPtr<cc::InputHandler>& input_handler);
+  ~UIScrollInputManager();
+
+  // Scroll the given |layer_to_scroll| according to |event|.
+  bool OnScrollEvent(const ScrollEvent& event, Layer* layer_to_scroll);
+
+ private:
+  std::unique_ptr<UIInputHandler> input_wrapper_;
+
+  DISALLOW_COPY_AND_ASSIGN(UIScrollInputManager);
+};
+
+}  // namespace ui
+
+#endif  // UI_COMPOSITOR_OVERSCROLL_UI_SCROLL_INPUT_MANAGER_H_