Force MimeHandlerView to always use BrowserPlugin

extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc

Index: extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
diff --git a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
index a58e021b4ba8fe95482c2d568067581fc057d036..34ded73d63e8a096766abf074b6cd5b0eded6183 100644
--- a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
+++ b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
@@ -82,6 +82,10 @@ MimeHandlerViewGuest::MimeHandlerViewGuest(WebContents* owner_web_contents)
 MimeHandlerViewGuest::~MimeHandlerViewGuest() {
 }
 
+bool MimeHandlerViewGuest::IsMimeHandlerViewGuest() {
+  return true;
+}
+
 const char* MimeHandlerViewGuest::GetAPINamespace() const {
   return "mimeHandlerViewGuestInternal";
 }