Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/pinch_zoom_scrollbar.h

Index: cc/pinch_zoom_scrollbar.h
diff --git a/cc/pinch_zoom_scrollbar.h b/cc/pinch_zoom_scrollbar.h
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+++ b/cc/pinch_zoom_scrollbar.h
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+// Copyright 2013 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_PINCH_ZOOM_SCROLLBAR_H_
+#define CC_PINCH_ZOOM_SCROLLBAR_H_
+
+#include "cc/cc_export.h"
+#include "third_party/WebKit/Source/Platform/chromium/public/WebScrollbar.h"
+
+namespace cc {
+
+class LayerTreeHost;
+
+class PinchZoomScrollbar : public WebKit::WebScrollbar {
+ public:
+  static const float kDefaultOpacity;
+  static const float kFadeDurationInSeconds;
+
+  PinchZoomScrollbar(
+      WebKit::WebScrollbar::Orientation orientation,
+      LayerTreeHost* owner);
+  virtual ~PinchZoomScrollbar() {}
+
+  // Implement WebKit::WebScrollbar.
+  virtual bool isOverlay() const;
+  virtual int value() const;
+  virtual WebKit::WebPoint location() const;
+  virtual WebKit::WebSize size() const;
+  virtual bool enabled() const;
+  virtual int maximum() const;
+  virtual int totalSize() const;
+  virtual bool isScrollViewScrollbar() const;
+  virtual bool isScrollableAreaActive() const;
+  virtual void getTickmarks(WebKit::WebVector<WebKit::WebRect>&) const {}
+  virtual WebKit::WebScrollbar::ScrollbarControlSize controlSize() const;
+  virtual WebKit::WebScrollbar::ScrollbarPart pressedPart() const;
+  virtual WebKit::WebScrollbar::ScrollbarPart hoveredPart() const;
+  virtual WebKit::WebScrollbar::ScrollbarOverlayStyle
+      scrollbarOverlayStyle() const;
+  virtual bool isCustomScrollbar() const;
+  virtual WebKit::WebScrollbar::Orientation orientation() const;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PinchZoomScrollbar);
+
+  WebKit::WebScrollbar::Orientation orientation_;
+  LayerTreeHost* owner_;
+};  // class PinchZoomScrollbar
+
+}  // namespace cc
+#endif // CC_PINCH_ZOOM_SCROLLBAR_H_