Allow a main interstitial frame to act as an ExtensionMessagePort opener

content/browser/frame_host/render_frame_host_delegate.h

Index: content/browser/frame_host/render_frame_host_delegate.h
diff --git a/content/browser/frame_host/render_frame_host_delegate.h b/content/browser/frame_host/render_frame_host_delegate.h
index ee5aae52bda611ff4eff5537c44a373a427dae52..a2a4c599c3a08322163ffcd221b80e5d0af492b7 100644
--- a/content/browser/frame_host/render_frame_host_delegate.h
+++ b/content/browser/frame_host/render_frame_host_delegate.h
@@ -31,6 +31,7 @@ class Message;
 
 namespace content {
 class GeolocationServiceContext;
+class InterstitialPage;
 class PageState;
 class RenderFrameHost;
 class WakeLockServiceContext;
@@ -116,6 +117,10 @@ class CONTENT_EXPORT RenderFrameHostDelegate {
   // not a WebContents, returns NULL.
   virtual WebContents* GetAsWebContents();
 
+  // Returns this object cast to an InterstitialPage if it is one. Returns
+  // nullptr otherwise.
+  virtual InterstitialPage* GetAsInterstitialPage();

[Charlie Reis, 2016/01/25 21:47:38]

Yeah, I suppose we can use this pattern again.  I'll be glad to see it go away
when interstitials are refactored to be committed pages, but it makes sense for
the time being.

[robwu, 2016/01/25 22:54:41]

Acknowledged.

+
   // The render frame has requested access to media devices listed in
   // |request|, and the client should grant or deny that permission by
   // calling |callback|.