RenderWidgetHostViewChildFrame's called a virtual in its ctor.

content/browser/frame_host/render_widget_host_view_guest.cc

Index: content/browser/frame_host/render_widget_host_view_guest.cc
diff --git a/content/browser/frame_host/render_widget_host_view_guest.cc b/content/browser/frame_host/render_widget_host_view_guest.cc
index 0c5f97b52cc41a56b2d0937512eb303bcb043275..cd85027fa29af2286ba4d268ea1518579772b4fb 100644
--- a/content/browser/frame_host/render_widget_host_view_guest.cc
+++ b/content/browser/frame_host/render_widget_host_view_guest.cc
@@ -76,6 +76,7 @@ RenderWidgetHostViewGuest::RenderWidgetHostViewGuest(
   gfx::NativeView view = GetNativeView();
   if (view)
     UpdateScreenInfo(view);
+  Init();

[clamy, 2016/10/05 12:35:53]

nit: For the sake of consistency, I think it'd be nicer to have a create
function that mirrors what is done in RenderWidgetHostViewChildFrame.

[dtapuska, 2016/10/05 14:25:00]

Done.

 }
 
 RenderWidgetHostViewGuest::~RenderWidgetHostViewGuest() {}