Made double-tap zoom work in pinch virtual viewport mode. (Blink-side)

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 75 matching lines @@
     void setSize(const IntSize&);
     IntSize size() const { return m_size; }
 
     // Resets the viewport to initial state.
     void reset();
 
     // Let the viewport know that the main frame changed size (either through screen
     // rotation on Android or window resize elsewhere).
     void mainFrameDidChangeSize();
 
+    // Sets scale without ensuring the viewport is within its bounds. Useful for
+    // situations when scale and offset are changing at the same time, e.g. during
+    // a compositor commit.
+    void setScaleWithoutClampingViewportOffset(float);
     void setScale(float);
     float scale() const { return m_scale; }
 
     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.
     FloatRect visibleRectInDocument() const;
 
     // Scroll the main frame and pinch viewport so that the given rect in the
     // top-level document is centered in the viewport. This method will avoid
     // scrolling the pinch viewport unless necessary.
     void scrollIntoView(const FloatRect&);
+
+    // Clamp the given point, in document coordinates, to the maximum/minimum
+    // scroll extents of the viewport within the document.
+    IntPoint clampDocumentOffsetAtScale(const IntPoint&, float);
+
 private:
     // ScrollableArea implementation
     virtual bool isActive() const OVERRIDE { return false; }
     virtual int scrollSize(ScrollbarOrientation) const OVERRIDE;
     virtual bool isScrollCornerVisible() const OVERRIDE { return false; }
     virtual IntRect scrollCornerRect() const OVERRIDE { return IntRect(); }
     virtual IntPoint scrollPosition() const OVERRIDE { return flooredIntPoint(m_offset); }
     virtual IntPoint minimumScrollPosition() const OVERRIDE;
     virtual IntPoint maximumScrollPosition() const OVERRIDE;
     virtual int visibleHeight() const OVERRIDE { return visibleRect().height(); };
@@ skipping 33 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;
 };
 
 } // namespace blink
 
 #endif // PinchViewport_h