Allow a main interstitial frame to act as an ExtensionMessagePort opener

content/public/browser/interstitial_page.h

Index: content/public/browser/interstitial_page.h
diff --git a/content/public/browser/interstitial_page.h b/content/public/browser/interstitial_page.h
index 71b8707e54dfa88395cecda7ce7c4cd794d65e06..51160120d10ace6959241440456f45f72d411cbe 100644
--- a/content/public/browser/interstitial_page.h
+++ b/content/public/browser/interstitial_page.h
@@ -53,6 +53,11 @@ class InterstitialPage {
   CONTENT_EXPORT static InterstitialPage* GetInterstitialPage(
       WebContents* web_contents);
 
+  // Retrieves the InterstitialPage that hosts the RenderFrameHost, or nullptr
+  // if |rfh| is not a part of any InterstitialPage.
+  CONTENT_EXPORT static InterstitialPage* FromRenderFrameHost(
+      RenderFrameHost* rfh);
+
   virtual ~InterstitialPage() {}
 
   // Shows the interstitial page in the tab.
@@ -85,6 +90,8 @@ class InterstitialPage {
 
   virtual InterstitialPageDelegate* GetDelegateForTesting() = 0;
   virtual void DontCreateViewForTesting() = 0;
+
+  virtual WebContents* web_contents() const = 0;

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

Style nit: We generally require CamelCase for virtual methods.

It'd be nice to avoid exposing this method if we can, since it becomes very easy
to forget that the interstitial's RFH and WebContents don't have a normal
relationship with each other (e.g., the RFH is not in the frame tree, and we
won't get the same WCO events for it).

I'm not sure if it's possible to avoid in your case or not, though.  If we do
keep it, let's put it above GetMainFrame and give some warning comments.

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

Done.

 };
 
 }  // namespace content