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 195 matching lines @@
     // If we're an embedded plugin we drop pinch-gestures to avoid zooming the
     // guest.
     return !is_full_page_plugin();
   }
   return false;
 }
 
 content::JavaScriptDialogManager*
 MimeHandlerViewGuest::GetJavaScriptDialogManager(
     WebContents* source) {
+  // WebContentsDelegates often service multiple WebContentses, and use the
+  // WebContents* parameter to tell which WebContents made the request. If we
+  // pass in our own pointer to the delegate call, the delegate will be asked,
+  // "What's the JavaScriptDialogManager of this WebContents for which you are
+  // not a delegate?" And it won't be able to answer that.
+  //
+  // So we pretend to be our owner WebContents, but only for the request to
+  // obtain the JavaScriptDialogManager. During calls to the
+  // JavaScriptDialogManager we will be honest about who we are.
   return owner_web_contents()->GetDelegate()->GetJavaScriptDialogManager(
-      web_contents());
+      owner_web_contents());
 }
 
 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