[DevTools] Use device metrics emulation implemented in content.

Source/web/WebViewImpl.h

Index: Source/web/WebViewImpl.h
diff --git a/Source/web/WebViewImpl.h b/Source/web/WebViewImpl.h
index 7e96a978da8417940d0a70fb24b221e9f87cbdea..5960cce0fbae6deeb8b0d5aed628b9d731c03be5 100644
--- a/Source/web/WebViewImpl.h
+++ b/Source/web/WebViewImpl.h
@@ -289,6 +289,7 @@ public:
     virtual bool inspectorSetting(const WebString& key, WebString* value) const;
     virtual void setInspectorSetting(const WebString& key,
                                      const WebString& value);
+    virtual void setDeviceEmulationParameters(bool enabled, float deviceScaleFactor, float rootLayerScale);
     virtual WebDevToolsAgent* devToolsAgent();
     virtual WebAXObject accessibilityObject();
     virtual void applyAutofillSuggestions(
@@ -628,6 +629,8 @@ private:
     void doPixelReadbackToCanvas(WebCanvas*, const WebCore::IntRect&);
     void reallocateRenderer();
     void updateLayerTreeViewport();
+    void updateRootLayerTransform();
+    void updateLayerTreeDeviceScaleFactor();
 
     // Helper function: Widens the width of |source| by the specified margins
     // while keeping it smaller than page width.
@@ -727,6 +730,9 @@ private:
 
     bool m_ignoreInputEvents;
 
+    float m_emulatedDeviceScaleFactor;
+    float m_rootLayerScale;
+
     // Webkit expects keyPress events to be suppressed if the associated keyDown
     // event was handled. Safari implements this behavior by peeking out the
     // associated WM_CHAR event if the keydown was handled. We emulate