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

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

Index: third_party/WebKit/Source/core/inspector/DevToolsHost.cpp
diff --git a/third_party/WebKit/Source/core/inspector/DevToolsHost.cpp b/third_party/WebKit/Source/core/inspector/DevToolsHost.cpp
index 9854ebcd4eceab5bc6d0963d9c4cf95c16c25015..6593eafab937d5552f7e7063a89b32029db99fba 100644
--- a/third_party/WebKit/Source/core/inspector/DevToolsHost.cpp
+++ b/third_party/WebKit/Source/core/inspector/DevToolsHost.cpp
@@ -164,16 +164,12 @@ void DevToolsHost::disconnectClient()
 
 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)