Bug 1562821 - Propagate nsIWebProgress events to the <xul:browser> in responsive design mode r=Ehsan

The work from bug 1510569 that has ported the majority of the `nsIWebProgress`
event handlers from `WebProgressChild`/`RemoteWebProgress` to
`BrowserChild`/`BrowserParent` was not properly propogating the events in the
responsive design mode case. The `BrowserParent` assumed that its frame element
was an `nsIBrowser`, but in RDM it is an `<iframe mozbrowser>` which does not
implement `nsIBrowser`. In the RDM case we now walk up the document in the
`BrowserParent` tree to find the `<xul:browser>` and call the event handlers on
that instead.

Differential Revision: https://phabricator.services.mozilla.com/D38916

--HG--
extra : moz-landing-system : lando

dom/ipc/BrowserParent.cpp

@@ -2582,8 +2582,23 @@ bool BrowserParent::GetWebProgressListener(
   MOZ_ASSERT(aOutManager);
   MOZ_ASSERT(aOutListener);
 
-  nsCOMPtr<nsIBrowser> browser =
-      mFrameElement ? mFrameElement->AsBrowser() : nullptr;
+  nsCOMPtr<nsIBrowser> browser;
+  RefPtr<Element> currentElement = mFrameElement;
+
+  // In Responsive Design Mode, mFrameElement will be the <iframe mozbrowser>,
+  // but we want the <xul:browser> that it is embedded in.
+  while (currentElement) {
+    browser = currentElement->AsBrowser();
+    if (browser) {
+      break;
+    }
+
+    BrowsingContext* browsingContext =
+        currentElement->OwnerDoc()->GetBrowsingContext();
+    currentElement =
+        browsingContext ? browsingContext->GetEmbedderElement() : nullptr;
+  }
+
   if (!browser) {
     return false;
   }