Bug 1562821 - Mirror RemoteWebNavigation state from the <xul:browser> to the <iframe mozbrowser> when in RDM r=ochameau

In the last patch of this series, I forgot to sync `remoteWebNavigationImpl`
state in the progress listener. This patch corrects that.

Differential Revision: https://phabricator.services.mozilla.com/D39395

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

devtools/client/responsive.html/browser/tunnel.js

@@ -112,6 +112,7 @@ function tunnelToInnerBrowser(outer, inner) {
         inner._imageDocument = outer._imageDocument;
         inner._isSyntheticDocument = outer._isSyntheticDocument;
         inner._innerWindowID = outer._innerWindowID;
+        inner._remoteWebNavigationImpl._currentURI = outer._remoteWebNavigationImpl._currentURI;
       }
     },