[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..066f32f543b35e57d8ad740a86268228cac03387 100644
--- a/third_party/WebKit/Source/core/inspector/DevToolsHost.cpp
+++ b/third_party/WebKit/Source/core/inspector/DevToolsHost.cpp
@@ -164,7 +164,10 @@ void DevToolsHost::disconnectClient()
 
 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)