Add a JavaScript dialog tab helper.

extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h"
 
 #include <utility>
 
 #include "base/strings/stringprintf.h"
 #include "components/guest_view/common/guest_view_constants.h"
@@ skipping 196 matching lines @@
     // guest.
     return !is_full_page_plugin();
   }
   return false;
 }
 
 content::JavaScriptDialogManager*
 MimeHandlerViewGuest::GetJavaScriptDialogManager(
     WebContents* source) {
   return owner_web_contents()->GetDelegate()->GetJavaScriptDialogManager(
-      web_contents());
+      owner_web_contents());

[raymes, 2016/09/01 01:28:30]

Could you explain why you've changed this? Thanks!

[Avi (use Gerrit), 2016/09/01 01:38:02]

Rather than having a single manager globally, I want to have the ability to have
the dialog code in a tab helper, living on the tab. And since the Browser is the
delegate for all of the tabs, the only way it knows which tab's tab helper to
use is that parameter.

Currently, the delegate gets the call "what's the dialog manager for this
WebContents that you're not delegate for?" With a global manager, that doesn't
matter, but with per-tab managers, that becomes a problem.

Once we have the manager, the guest WebContents can pass its pointer to the
manager, but to get the manager itself the guest WebContents has to pretend that
it's its parent, because the delegate doesn't know that the guest WebContents
exists.

[paulmeyer, 2016/09/01 15:45:53]

Nit: Could you please add a short comment here to this effect? (particularly
about the guest pretending to be its parent and why)

 }
 
 bool MimeHandlerViewGuest::SaveFrame(const GURL& url,
                                      const content::Referrer& referrer) {
   if (!attached())
     return false;
 
   embedder_web_contents()->SaveFrame(stream_->stream_info()->original_url,
                                      referrer);
   return true;
 }
 
 void MimeHandlerViewGuest::DocumentOnLoadCompletedInMainFrame() {
   // Assume the embedder WebContents is valid here.
   DCHECK(embedder_web_contents());
 
   embedder_web_contents()->Send(
       new ExtensionsGuestViewMsg_MimeHandlerViewGuestOnLoadCompleted(
           element_instance_id()));
 }
 
 base::WeakPtr<StreamContainer> MimeHandlerViewGuest::GetStream() const {
   if (!stream_)
     return base::WeakPtr<StreamContainer>();
   return stream_->GetWeakPtr();
 }
 
 }  // namespace extensions