[DevTools] Handle emulated device scale factor and original device scale factor properly.

third_party/WebKit/Source/core/inspector/DevToolsHost.cpp

 /*
  * Copyright (C) 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Matt Lilek <webkit@mattlilek.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 146 matching lines @@
     m_client = 0;
     if (m_menuProvider) {
         m_menuProvider->disconnect();
         m_menuProvider = nullptr;
     }
     m_frontendFrame = nullptr;
 }
 
 float DevToolsHost::zoomFactor()
 {
-    return m_frontendFrame ? m_frontendFrame->pageZoomFactor() : 1;
+    float zoomFactor = m_frontendFrame->pageZoomFactor();
+    // Cancel the device scale factor applied to the zoom factor in
+    // use-zoom-for-dsf mode.
+    return convertLengthForEmbedder(1000.f * zoomFactor) / 1000.f;
 }
 
 float DevToolsHost::convertLengthForEmbedder(float length)
 {
     if (!m_frontendFrame)
         return length;
     const HostWindow* hostWindow = m_frontendFrame->view()->hostWindow();
     IntRect screen = hostWindow->viewportToScreen(IntRect(0, 0, length, 0));
     return screen.width();
 }
@@ skipping 64 matching lines @@
 {
     return m_client && m_client->isUnderTest();
 }
 
 bool DevToolsHost::isHostedMode()
 {
     return false;
 }
 
 } // namespace blink