[DevTools] Use device metrics emulation implemented in content.

Source/web/WebDevToolsAgentPrivate.h

Index: Source/web/WebDevToolsAgentPrivate.h
diff --git a/Source/web/WebDevToolsAgentPrivate.h b/Source/web/WebDevToolsAgentPrivate.h
index 2c57e0f6d637f0d0e784c436fcb54507cf51990a..87333fee6e0e10484ecc2d13398850580fb24d88 100644
--- a/Source/web/WebDevToolsAgentPrivate.h
+++ b/Source/web/WebDevToolsAgentPrivate.h
@@ -47,13 +47,6 @@ public:
     // in this context should be done here.
     virtual void didCreateScriptContext(WebFrameImpl*, int worldId) = 0;
 
-    // A new FrameView has been created for the specified WebFrame using
-    // the Frame::createView() call.
-    virtual void mainFrameViewCreated(WebFrameImpl*) = 0;
-
-    // Returns true if the device metrics override mode is enabled.
-    virtual bool metricsOverridden() = 0;
-
     // WebViewImpl has been resized.
     virtual void webViewResized(const WebSize&) = 0;