Bug 1514360 - Add nsIWindowMediator.getMostRecentBrowserWindow() r=Ehsan

We currently don't use 'navigator:browser' for GeckoView windows because
we need an easy way to disambiguate from Fennec windows. Instead, we use
'navigator:geckoview' for those windows. This adds a method that falls
back to that automatically, useful in cases where you want it to work on
both Desktop/Fennec and GeckoView.

Differential Revision: https://phabricator.services.mozilla.com/D14613

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

xpfe/appshell/nsIWindowMediator.idl

@@ -66,6 +66,13 @@ interface nsIWindowMediator: nsISupports
     */
   mozIDOMWindowProxy getMostRecentWindow(in wstring aWindowType);
 
+  /** This is a shortcut for getMostRecentWindow('navigator:browser'), but
+    * it also tries 'navigator:geckoview' if that fails.
+    *
+    * @return the topmost browser window
+    */
+  mozIDOMWindowProxy getMostRecentBrowserWindow();
+
   /**
    * Same as getMostRecentWindow, but ignores private browsing
    * windows.

xpfe/appshell/nsWindowMediator.cpp

@@ -236,6 +236,21 @@ nsWindowMediator::GetMostRecentWindow(const char16_t* inType,
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsWindowMediator::GetMostRecentBrowserWindow(mozIDOMWindowProxy** outWindow) {
+  nsresult rv = GetMostRecentWindow(u"navigator:browser", outWindow);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+#ifdef MOZ_WIDGET_ANDROID
+  if (!*outWindow) {
+    rv = GetMostRecentWindow(u"navigator:geckoview", outWindow);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+#endif
+
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsWindowMediator::GetMostRecentNonPBWindow(const char16_t* aType,
                                            mozIDOMWindowProxy** aWindow) {