Pass the device scale factor in the command line to renderer processes.

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 0770a14b29967b08247e43848b050041350a0898..62d4d511db5dd5d95e5ae75a99a5225ec2a781f0 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -410,6 +410,9 @@ const char kEnableHighDpiCompositingForFixedPosition[] =
      "enable-high-dpi-fixed-position-compositing";
 
 #if defined(OS_WIN)
+// Device scale factor passed to certain processes like renderers, etc.
+const char kDeviceScaleFactor[]     = "device-scale-factor";
+
 // Disable the Legacy Window which corresponds to the size of the WebContents.
 const char kDisableLegacyIntermediateWindow[] = "disable-legacy-window";