Add touchpad pinch zoom support to Blink

Source/core/frame/PinchViewport.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 88 matching lines @@
 
     // Let the viewport know that the main frame changed size (either through screen
     // rotation on Android or window resize elsewhere).
     void mainFrameDidChangeSize();
 
     // Sets scale and location in one operation, preventing intermediate clamping.
     void setScaleAndLocation(float scale, const FloatPoint& location);
     void setScale(float);
     float scale() const { return m_scale; }
 
+    // Update scale factor, magnifying or minifying by magnifyDelta, centered around
+    // the point specified by anchor in window coordinates. Returns false if page
+    // scale factor is left unchanged.
+    bool magnifyScaleAroundAnchor(float magnifyDelta, const FloatPoint& anchor);
+
     void registerLayersWithTreeView(blink::WebLayerTreeView*) const;
     void clearLayersForTreeView(blink::WebLayerTreeView*) const;
 
     // The portion of the unzoomed frame visible in the inner "pinch" viewport,
     // in partial CSS pixels. Relative to the main frame.
     FloatRect visibleRect() const;
 
     // The viewport rect relative to the document origin, in partial CSS pixels.
     // FIXME: This should be a DoubleRect since scroll offsets are now doubles.
     FloatRect visibleRectInDocument() const;
@@ skipping 81 matching lines @@
     // Offset of the pinch viewport from the main frame's origin, in CSS pixels.
     FloatPoint m_offset;
     float m_scale;
     IntSize m_size;
     float m_topControlsAdjustment;
 };
 
 } // namespace blink
 
 #endif // PinchViewport_h