Correct callback arity in |attachImpl$| for OOPIF based guests.

In the OOPIF based guest version of |attachImpl$| the callback for
|AttachIframeGuest| takes "contentWindow" as an argument, but
|GuestViewAttachIframeRequest::HandleResponse| does not call it
with any arguments.

Bug: None
Change-Id: I9ab5a719814fff549f6d6880d63aba39489cfeae
Reviewed-on: https://chromium-review.googlesource.com/861183
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Commit-Queue: Kevin McNee <mcnee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528631}

extensions/renderer/resources/guest_view/guest_view_iframe.js

@@ -38,12 +38,11 @@ GuestViewImpl.prototype.attachImpl$ = function(
     return;
   }
 
-  // Callback wrapper function to store the contentWindow from the attachGuest()
+  // Callback wrapper function to set the contentWindow following attachment,
-  // callback, handle potential attaching failure, register an automatic detach,
   // and advance the queue.
-  var callbackWrapper = function(callback, contentWindow) {
+  var callbackWrapper = function(callback) {
+    var contentWindow = getIframeContentWindow(viewInstanceId);
     // Check if attaching failed.
-    contentWindow = getIframeContentWindow(viewInstanceId);
     if (!contentWindow) {
       this.state = GuestViewImpl.GuestState.GUEST_STATE_CREATED;
       this.internalInstanceId = 0;