[DevTools] Explicitly enable/disable Page.viewportChanged protocol event.

Source/core/inspector/InspectorPageAgent.cpp

 /*
  * Copyright (C) 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 1148 matching lines @@
 
 void InspectorPageAgent::didScroll()
 {
     if (m_enabled)
         m_overlay->update();
     viewportChanged();
 }
 
 void InspectorPageAgent::viewportChanged()
 {
-    if (!m_enabled)
+    if (!m_enabled || !m_deviceMetricsOverridden)
         return;
     IntSize contentsSize = m_page->deprecatedLocalMainFrame()->view()->contentsSize();
     IntRect viewRect = m_page->deprecatedLocalMainFrame()->view()->visibleContentRect();
     RefPtr<TypeBuilder::Page::Viewport> viewport = TypeBuilder::Page::Viewport::create()
         .setScrollX(viewRect.x())
         .setScrollY(viewRect.y())
         .setContentsWidth(contentsSize.width())
         .setContentsHeight(contentsSize.height())
         .setPageScaleFactor(m_page->pageScaleFactor());
     m_frontend->viewportChanged(viewport);
@@ skipping 247 matching lines @@
 bool InspectorPageAgent::getEditedResourceContent(const String& url, String* content)
 {
     if (!m_editedResourceContent.contains(url))
         return false;
     *content = m_editedResourceContent.get(url);
     return true;
 }
 
 } // namespace WebCore