[DevTools] Use device metrics emulation implemented in content.

Source/core/page/FrameView.h

Index: Source/core/page/FrameView.h
diff --git a/Source/core/page/FrameView.h b/Source/core/page/FrameView.h
index 81c9895520b5be611b611437bf866f2d96001c34..3813791f7e9c6066945afa3853a9f5c155cadf91 100644
--- a/Source/core/page/FrameView.h
+++ b/Source/core/page/FrameView.h
@@ -155,6 +155,9 @@ public:
     virtual float visibleContentScaleFactor() const OVERRIDE { return m_visibleContentScaleFactor; }
     void setVisibleContentScaleFactor(float);
 
+    virtual float inputEventsScaleFactor() const OVERRIDE { return visibleContentScaleFactor() * m_inputEventsScaleFactorForEmulation; }
+    void setInputEventsScaleFactorForEmulation(float);
+
     virtual void setScrollPosition(const IntPoint&) OVERRIDE;
     virtual void repaintFixedElementsAfterScrolling();
     virtual void updateFixedElementsAfterScrolling();
@@ -536,6 +539,7 @@ private:
     bool m_hasSoftwareFilters;
 
     float m_visibleContentScaleFactor;
+    float m_inputEventsScaleFactorForEmulation;
 
     PartialLayoutState m_partialLayout;
 };