Bug 1442334 - Remove redundant binding change in RDM. r=ochameau

RDM was explicitly forcing the remote browser XBL binding via inline style, but
that's actually redunant with what you'd get via CSS.  (I am unsure if that's
always been true...)

It appears we can safely remove this to reduce some complexity here.

MozReview-Commit-ID: 2xlS6Dd2VYj

--HG--
extra : rebase_source : 2f9eb8789650e96cf82be60e7fe07d2bb3159a91

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

@@ -164,6 +164,12 @@ function tunnelToInnerBrowser(outer, inner) {
       // even though it's not true.  Since the actions the browser UI performs are sent
       // down to the inner browser by this tunnel, the tab's remoteness effectively is the
       // remoteness of the inner browser.
+      // Setting this attribute changes the browser to the remote XBL binding via CSS.
+      // The XBL binding for remote browsers uses the message manager for many actions in
+      // the UI and that works well here, since it gives us one main thing we need to
+      // route to the inner browser (the messages), instead of having to tweak many
+      // different browser properties.  It is safe to alter a XBL binding dynamically.
+      // The content within is not reloaded.
       outer.setAttribute("remote", "true");
       outer.setAttribute("remoteType", inner.remoteType);
 
@@ -171,13 +177,6 @@ function tunnelToInnerBrowser(outer, inner) {
       // such as form fill controllers.  Otherwise they will remain in place and leak the
       // outer docshell.
       outer.destroy();
-      // The XBL binding for remote browsers uses the message manager for many actions in
-      // the UI and that works well here, since it gives us one main thing we need to
-      // route to the inner browser (the messages), instead of having to tweak many
-      // different browser properties.  It is safe to alter a XBL binding dynamically.
-      // The content within is not reloaded.
-      outer.style.MozBinding = "url(chrome://browser/content/tabbrowser.xml" +
-                               "#tabbrowser-remote-browser)";
 
       // The constructor of the new XBL binding is run asynchronously and there is no
       // event to signal its completion.  Spin an event loop to watch for properties that
@@ -185,6 +184,10 @@ function tunnelToInnerBrowser(outer, inner) {
       Services.tm.spinEventLoopUntil(() => {
         return outer._remoteWebNavigation;
       });
+      // Verify that we indeed have the correct binding.
+      if (!outer.isRemoteBrowser) {
+        throw new Error("Browser failed to switch to remote browser binding");
+      }
 
       // Replace the `webNavigation` object with our own version which tries to use
       // mozbrowser APIs where possible.  This replaces the webNavigation object that the
@@ -279,7 +282,6 @@ function tunnelToInnerBrowser(outer, inner) {
 
       // Reset the XBL binding back to the default.
       outer.destroy();
-      outer.style.MozBinding = "";
 
       // Reset @remote since this is now back to a regular, non-remote browser
       outer.setAttribute("remote", "false");