Allow MimeHandlerViewGuest be embedded inside OOPIFs

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 2c924c11328d8a8c7bf855becdf71d32cff164e9..1a078fd509297b82045cc337f6f2bdb1aace129a 100644
--- a/content/browser/frame_host/render_widget_host_view_guest.cc
+++ b/content/browser/frame_host/render_widget_host_view_guest.cc
@@ -601,6 +601,10 @@ bool RenderWidgetHostViewGuest::IsRenderWidgetHostViewGuest() {
   return true;
 }
 
+RenderWidgetHostViewBase* RenderWidgetHostViewGuest::GetOuterView() {
+  return GetOwnerRenderWidgetHostView();
+}
+
 void RenderWidgetHostViewGuest::OnHandleInputEvent(
     RenderWidgetHostImpl* embedder,
     int browser_plugin_instance_id,