Allow MimeHandlerViewGuest be embedded inside OOPIFs

extensions/browser/guest_view/extensions_guest_view_message_filter.cc

Index: extensions/browser/guest_view/extensions_guest_view_message_filter.cc
diff --git a/extensions/browser/guest_view/extensions_guest_view_message_filter.cc b/extensions/browser/guest_view/extensions_guest_view_message_filter.cc
index 9dea442edf213b69d205ac770f3f5194607f7add..781997c64feb62fc8f93d97dd528153fe2cc731c 100644
--- a/extensions/browser/guest_view/extensions_guest_view_message_filter.cc
+++ b/extensions/browser/guest_view/extensions_guest_view_message_filter.cc
@@ -169,15 +169,16 @@ void ExtensionsGuestViewMessageFilter::MimeHandlerViewGuestCreatedCallback(
   if (!rfh)
     return;
 
+  guest_view->SetEmbedderFrame(embedder_render_process_id,

[wjmaclean, 2016/10/20 14:47:22]

Will it ever be the case that we'll want to move a guest from the embedder in
which it was originally created to another embedder? I'm guessing not, but if it
can happen, do we need a mechanism to update these values on the guest_view?

[EhsanK, 2016/10/20 21:41:18]

Interesting point. But 1) I am not quite sure how we can detach from on frame
into another when they are cross process. 2) If we can, then I believe the
BrowserPluginGuest::OnDetach is called which will check
if the guest can run in detached mode (CanRunInDetachedState()). The answer is
no for MimeHandlerViewGuest which is the guest type here.

Having said this, I think we should be careful with referencing RFH
(GetEmbedderFrame). For other guest types it should be safe since I am getting
it from owner_web_contents(). For MimeHandlerView I will investigate to see if
it is possible for the view to outlive its embedding frame (I guess not since it
is an element after all, but I am not sure enough).

+                               embedder_render_frame_id);
+
   base::DictionaryValue attach_params;
   attach_params.SetInteger(guest_view::kElementWidth, element_size.width());
   attach_params.SetInteger(guest_view::kElementHeight, element_size.height());
   auto* manager = GuestViewManager::FromBrowserContext(browser_context_);
   CHECK(manager);
-  manager->AttachGuest(embedder_render_process_id,
-                       element_instance_id,
-                       guest_instance_id,
-                       attach_params);
+  manager->AttachGuest(embedder_render_process_id, element_instance_id,
+                       guest_instance_id, attach_params);
 
   rfh->Send(
       new ExtensionsGuestViewMsg_CreateMimeHandlerViewGuestACK(