Bug 1499067 - Stub implementation of BrowserApp.closeTab for GeckoView. r=snorp

Differential Revision: https://phabricator.services.mozilla.com/D11121

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

mobile/android/modules/geckoview/GeckoViewTab.jsm

@@ -30,6 +30,10 @@ class GeckoViewTab extends GeckoViewModule {
       tabs: [tab],
       selectedTab: tab,
 
+      closeTab: function(aTab) {
+        // not implemented
+      },
+
       getTabForId: function(aId) {
         return this.selectedTab;
       },