Bug 1441284 - Part 2 - Remove the "_currentSubView" property. r=Gijs

MozReview-Commit-ID: Aua3V8hOT39

--HG--
extra : rebase_source : 08d506c3d65b3e2e72532183e776f8aa1c6c0975

browser/components/customizableui/PanelMultiView.jsm

@@ -380,12 +380,6 @@ var PanelMultiView = class extends this.AssociatedToNode {
                                     .getService(Ci.nsIScreenManager);
   }
 
-  get _currentSubView() {
-    // Peek the top of the stack, but fall back to the main view if the list of
-    // opened views is currently empty.
-    let panelView = this.openViews[this.openViews.length - 1];
-    return (panelView && panelView.node) || this._mainView;
-  }
   get showingSubView() {
     return this.openViews.length > 1;
   }
@@ -1108,8 +1102,11 @@ var PanelMultiView = class extends this.AssociatedToNode {
     switch (aEvent.type) {
       case "keydown":
         if (!this._transitioning) {
-          PanelView.forNode(this._currentSubView)
-                   .keyNavigation(aEvent, this._dir);
+          // Since we start listening for the "keydown" event when the popup is
+          // already showing and stop listening when the panel is hidden, we
+          // always have at least one view open.
+          let currentView = this.openViews[this.openViews.length - 1];
+          currentView.keyNavigation(aEvent, this._dir);
         }
         break;
       case "mousemove":