Sets a transparent background for out-of-process subframes.

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index a7bf289d27d17651a50b790bc45ba742111eab0d..fd5d07633084edff1460a3a1a548feb05f01a317 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -58,6 +58,7 @@ class SyncMessageFilter;
 
 namespace blink {
 struct WebDeviceEmulationParams;
+class WebFrameWidget;
 class WebGestureEvent;
 class WebLocalFrame;
 class WebMouseEvent;
@@ -374,8 +375,9 @@ class CONTENT_EXPORT RenderWidget
 
   ~RenderWidget() override;
 
-  static blink::WebWidget* CreateWebFrameWidget(RenderWidget* render_widget,
-                                                blink::WebLocalFrame* frame);
+  static blink::WebFrameWidget* CreateWebFrameWidget(
+      RenderWidget* render_widget,
+      blink::WebLocalFrame* frame);
 
   // Creates a WebWidget based on the popup type.
   static blink::WebWidget* CreateWebWidget(RenderWidget* render_widget);