[DevTools] Allow overriding only the device scale factor.

Source/web/WebDevToolsAgentImpl.cpp

 /*
  * Copyright (C) 2010-2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 306 matching lines @@
     }
     if (WebInputEvent::isKeyboardEventType(inputEvent.type)) {
         PlatformKeyboardEvent keyboardEvent = PlatformKeyboardEventBuilder(*static_cast<const WebKeyboardEvent*>(&inputEvent));
         return ic->handleKeyboardEvent(page->mainFrame(), keyboardEvent);
     }
     return false;
 }
 
 void WebDevToolsAgentImpl::overrideDeviceMetrics(int width, int height, float deviceScaleFactor, bool emulateViewport, bool fitWindow)
 {
-    if (!width && !height) {
+    if (!width && !height && !deviceScaleFactor) {
         if (m_deviceMetricsEnabled) {
             m_deviceMetricsEnabled = false;
             m_webViewImpl->setBackgroundColorOverride(Color::transparent);
             RuntimeEnabledFeatures::setOverlayScrollbarsEnabled(m_isOverlayScrollbarsEnabled);
             disableViewportEmulation();
             m_client->disableDeviceEmulation();
         }
     } else {
         if (!m_deviceMetricsEnabled) {
             m_deviceMetricsEnabled = true;
@@ skipping 326 matching lines @@
         || commandName == InspectorBackendDispatcher::commandName(InspectorBackendDispatcher::kProfiler_startCmd)
         || commandName == InspectorBackendDispatcher::commandName(InspectorBackendDispatcher::kProfiler_stopCmd);
 }
 
 void WebDevToolsAgent::processPendingMessages()
 {
     PageScriptDebugServer::shared().runPendingTasks();
 }
 
 } // namespace blink