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

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 98e45d6a13a3609dcd123f443c7b52a23bcfe362..5490265b497500b230ba1bbe9ed93d57a1143f08 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -165,9 +165,11 @@
 #endif
 
 #if defined(OS_WIN)
+#include "base/strings/string_number_conversions.h"
 #include "base/win/scoped_com_initializer.h"
 #include "content/common/font_cache_dispatcher_win.h"
 #include "content/common/sandbox_win.h"
+#include "ui/gfx/win/dpi.h"
 #endif
 
 #if defined(ENABLE_WEBRTC)
@@ -1037,6 +1039,11 @@ void RenderProcessHostImpl::AppendRendererCommandLine(
   if (content::IsPinchToZoomEnabled())
     command_line->AppendSwitch(switches::kEnablePinch);
 
+#if defined(OS_WIN)
+  command_line->AppendSwitchASCII(switches::kDeviceScaleFactor,
+                                  base::DoubleToString(gfx::GetDPIScale()));
+#endif
+
   AppendCompositorCommandLineFlags(command_line);
 }