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

Source/web/WebViewImpl.h

Index: Source/web/WebViewImpl.h
diff --git a/Source/web/WebViewImpl.h b/Source/web/WebViewImpl.h
index aa402ad54de27914f62986ff15f22e0e353923d5..45c33154ade2b024281cc6667fa82d7e862b58e4 100644
--- a/Source/web/WebViewImpl.h
+++ b/Source/web/WebViewImpl.h
@@ -481,6 +481,8 @@ public:
     // Returns the bounding box of the block type node touched by the WebRect.
     WebRect computeBlockBounds(const WebRect&, bool ignoreClipping);
 
+    // FIXME(bokan): Replace with PinchViewport::clampDocumentOffsetAtScale once
+    // old-path is gone.
     IntPoint clampOffsetAtScale(const IntPoint& offset, float scale);
 
     // Exposed for tests.
@@ -498,6 +500,7 @@ private:
     // TODO(bokan): Remains for legacy pinch. Remove once it's gone. Made private to
     // prevent external usage
     virtual void setPageScaleFactor(float scaleFactor, const WebPoint& origin) OVERRIDE;
+    void setPageScaleFactorFromImpl(float);
 
     float legibleScale() const;
     void refreshPageScaleFactorAfterLayout();