Fix mime-handler-view crash upon creation:

extensions/renderer/guest_view/guest_view_container.cc

Index: extensions/renderer/guest_view/guest_view_container.cc
diff --git a/extensions/renderer/guest_view/guest_view_container.cc b/extensions/renderer/guest_view/guest_view_container.cc
index b31ba8d2214b80ee5e1b468718bcde3ba8a95853..781027063a16d8079aa3dc2de2d08a7222e5c59d 100644
--- a/extensions/renderer/guest_view/guest_view_container.cc
+++ b/extensions/renderer/guest_view/guest_view_container.cc
@@ -148,6 +148,12 @@ void GuestViewContainer::OnCreateMimeHandlerViewGuestACK(
 void GuestViewContainer::OnGuestAttached(int element_instance_id,
                                          int guest_proxy_routing_id) {
   attached_ = true;
+
+  if (!mime_type_.empty()) {
+    // MimeHandlerView's creation and attachment is not done via JS API.
+    return;
+  }
+
   // Handle the callback for the current request with a pending response.
   HandlePendingResponseCallback(guest_proxy_routing_id);
   // Perform the subsequent attach request if one exists.