[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;

[tkent, 2016/03/03 13:05:55]

The original code implies m_fontendFrame can be nullptr.  Is it ok to remove the
nullptr check?

[oshima, 2016/03/03 14:20:55]

Good point. Done.

-}
-
-float DevToolsHost::convertLengthForEmbedder(float length)
-{
-    if (!m_frontendFrame)
-        return length;
+    float zoomFactor = m_frontendFrame->pageZoomFactor();
+    // Cancel the device scale factor applied to the zoom factor in
+    // use-zoom-for-dsf mode.
     const HostWindow* hostWindow = m_frontendFrame->view()->hostWindow();
-    IntRect screen = hostWindow->viewportToScreen(IntRect(0, 0, length, 0));
-    return screen.width();
+    float windowToViewportRatio = hostWindow->windowToViewportScalar(1.0f);
+    return zoomFactor / windowToViewportRatio;
 }
 
 void DevToolsHost::setInjectedScriptForOrigin(const String& origin, const String& script)
 {
     if (m_client)
         m_client->setInjectedScriptForOrigin(origin, script);
 }
 
 void DevToolsHost::copyText(const String& text)
 {
@@ skipping 55 matching lines @@
 {
     return m_client && m_client->isUnderTest();
 }
 
 bool DevToolsHost::isHostedMode()
 {
     return false;
 }
 
 } // namespace blink