refactor(tabs): prevent unnecessary updates during destroy

If the containing ionTabs directive is being destroyed, then child
ionTab directives should not don't bother going through its
controller’s `remove` method, which selects a new active tab as each
ionTab is being destroyed. By selecting a new active tab as each tab is
removed, it causes unnecessary view loads, transitions and multiple
`viewState.changeHistory` events.

js/angular/directive/tab.js

@@ -98,7 +98,13 @@ function($rootScope, $animate, $ionicBind, $compile) {
 
         tabsCtrl.add($scope);
         $scope.$on('$destroy', function() {
-          tabsCtrl.remove($scope);
+          if(!$scope.$tabsDestory) {
+            // if the containing ionTabs directive is being destroyed
+            // then don't bother going through the controllers remove
+            // method, since remove will reset the active tab as each tab
+            // is being destroyed, causing unnecessary view loads and transitions
+            tabsCtrl.remove($scope);
+          }
           tabNavElement.isolateScope().$destroy();
           tabNavElement.remove();
         });

js/angular/directive/tabs.js

@@ -50,9 +50,9 @@ IonicModule.constant('$ionicTabsConfig', {
 
 IonicModule
 .directive('ionTabs', [
-  '$ionicViewService', 
-  '$ionicTabsDelegate', 
-  '$ionicTabsConfig', 
+  '$ionicViewService',
+  '$ionicTabsDelegate',
+  '$ionicTabsConfig',
 function($ionicViewService, $ionicTabsDelegate, $ionicTabsConfig) {
   return {
     restrict: 'E',
@@ -74,7 +74,14 @@ function($ionicViewService, $ionicTabsDelegate, $ionicTabsConfig) {
           tabsCtrl, $attr.delegateHandle
         );
 
-        $scope.$on('$destroy', deregisterInstance);
+        $scope.$on('$destroy', function(){
+          // variable to inform child tabs that they're all being blown away
+          // used so that while destorying an individual tab, each one
+          // doesn't select the next tab as the active one, which causes unnecessary
+          // loading of tab views when each will eventually all go away anyway
+          $scope.$tabsDestory = true;
+          deregisterInstance();
+        });
 
         tabsCtrl.$scope = $scope;
         tabsCtrl.$element = $element;