[Pinch-to-zoom] Moved scale factor into PinchViewport

Source/core/frame/FrameHost.h

Index: Source/core/frame/FrameHost.h
diff --git a/Source/core/frame/FrameHost.h b/Source/core/frame/FrameHost.h
index 99fb15eee657143e6f9174bbbcda9e20a15193e9..ee1ad1466ce8e7677b2d6dd06091414d88dbbd0f 100644
--- a/Source/core/frame/FrameHost.h
+++ b/Source/core/frame/FrameHost.h
@@ -74,14 +74,14 @@ public:
     // This value does not account for Page zoom, use LocalFrame::devicePixelRatio instead.
     float deviceScaleFactor() const;
 
-    PinchViewport& pinchViewport();
+    PinchViewport& pinchViewport() const;
 
 private:
     explicit FrameHost(Page&);
 
     Page& m_page;
     const OwnPtr<PageConsole> m_console;
-    PinchViewport m_pinchViewport;
+    const OwnPtr<PinchViewport> m_pinchViewport;
 };
 
 }