Add touchpad pinch zoom support to Blink

Source/core/page/ChromeClient.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple, Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 127 matching lines @@
     virtual void setCursor(const Cursor&) = 0;
     virtual void scheduleAnimation() = 0;
     // End methods used by HostWindow.
 
     virtual void scheduleAnimationForFrame(LocalFrame*) { }
 
     virtual void dispatchViewportPropertiesDidChange(const ViewportDescription&) const { }
 
     virtual void contentsSizeChanged(LocalFrame*, const IntSize&) const = 0;
     virtual void pageScaleFactorChanged() const { }
+    virtual float clampPageScaleFactorToLimits(float scale) const { return scale; }
     virtual void layoutUpdated(LocalFrame*) const { }
 
     virtual void mouseDidMoveOverElement(const HitTestResult&) = 0;
 
     virtual void setToolTip(const String&, TextDirection) = 0;
 
     virtual void print(LocalFrame*) = 0;
 
     virtual void annotatedRegionsChanged() = 0;
 
@@ skipping 75 matching lines @@
 
     virtual void showUnhandledTapUIIfNeeded(IntPoint, Node*, bool) { }
 
 protected:
     virtual ~ChromeClient() { }
 };
 
 } // namespace blink
 
 #endif // ChromeClient_h