Get the default device scale factor from monitor

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index d31126bf3642cd27a150f1735d3b6e17d8c47ea4..e149c4e952bca00abad5fbde2a09328683a3d0f9 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -58,6 +58,8 @@
 #include "content/public/common/content_restriction.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/url_constants.h"
+#include "ui/gfx/monitor.h"
+#include "ui/gfx/screen.h"
 #include "net/base/mime_util.h"
 #include "net/base/net_util.h"
 #include "net/base/network_change_notifier.h"
@@ -505,12 +507,14 @@ WebPreferences WebContentsImpl::GetWebkitPrefs(RenderViewHost* rvh,
     prefs.accelerated_2d_canvas_enabled = false;
   }
 
-  int default_device_scale_factor;
-  base::StringToInt(command_line.GetSwitchValueASCII(
-                        switches::kDefaultDeviceScaleFactor),
-                    &default_device_scale_factor);
-
-  prefs.default_device_scale_factor = default_device_scale_factor;
+  if (rvh->GetView()) {
+    gfx::Monitor monitor = gfx::Screen::GetMonitorNearestWindow(
+        rvh->GetView()->GetNativeView());
+    prefs.default_device_scale_factor =
+        static_cast<int>(monitor.device_scale_factor());
+  } else {
+    prefs.default_device_scale_factor = 1;
+  }
 
   content::GetContentClient()->browser()->OverrideWebkitPrefs(rvh, url, &prefs);