Add delegate to install web_contents helpers for MimeHandlerView.

extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h

Index: extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h
diff --git a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h
index 3eff421b3c74155ccc68581912d400742180cb17..ac7b6fee6afba05d4efcd8f12c639aab6940f9ee 100644
--- a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h
+++ b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.h
@@ -9,6 +9,8 @@
 
 namespace extensions {
 
+class MimeHandlerViewGuestDelegate;
+
 class MimeHandlerViewGuest : public GuestView<MimeHandlerViewGuest> {
  public:
   static GuestViewBase* Create(content::BrowserContext* browser_context,
@@ -25,6 +27,7 @@ class MimeHandlerViewGuest : public GuestView<MimeHandlerViewGuest> {
       const base::DictionaryValue& create_params,
       const WebContentsCreatedCallback& callback) OVERRIDE;
   virtual void DidAttachToEmbedder() OVERRIDE;
+  virtual void DidInitialize() OVERRIDE;
 
   // WebContentsDelegate implementation.
   virtual void HandleKeyboardEvent(
@@ -36,6 +39,8 @@ class MimeHandlerViewGuest : public GuestView<MimeHandlerViewGuest> {
                        int guest_instance_id);
   virtual ~MimeHandlerViewGuest();
 
+  scoped_ptr<MimeHandlerViewGuestDelegate> delegate_;
+
   DISALLOW_COPY_AND_ASSIGN(MimeHandlerViewGuest);
 };