fix(rootScope): prevent memory leak when destroying scopes

Closes #11173
Closes #11169

src/ng/rootScope.js

@@ -80,9 +80,27 @@ function $RootScopeProvider() {
     return TTL;
   };
 
+  function createChildScopeClass(parent) {
+    function ChildScope() {
+      this.$$watchers = this.$$nextSibling =
+          this.$$childHead = this.$$childTail = null;
+      this.$$listeners = {};
+      this.$$listenerCount = {};
+      this.$$watchersCount = 0;
+      this.$id = nextUid();
+      this.$$ChildScope = null;
+    }
+    ChildScope.prototype = parent;
+    return ChildScope;
+  }
+
   this.$get = ['$injector', '$exceptionHandler', '$parse', '$browser',
       function($injector, $exceptionHandler, $parse, $browser) {
 
+    function destroyChildScope($event) {
+        $event.currentScope.$$destroyed = true;
+    }
+
     /**
      * @ngdoc type
      * @name $rootScope.Scope
@@ -205,15 +223,7 @@ function $RootScopeProvider() {
           // Only create a child scope class if somebody asks for one,
           // but cache it to allow the VM to optimize lookups.
           if (!this.$$ChildScope) {
-            this.$$ChildScope = function ChildScope() {
-              this.$$watchers = this.$$nextSibling =
-                  this.$$childHead = this.$$childTail = null;
-              this.$$listeners = {};
-              this.$$listenerCount = {};
-              this.$id = nextUid();
-              this.$$ChildScope = null;
-            };
-            this.$$ChildScope.prototype = this;
+            this.$$ChildScope = createChildScopeClass(this);
           }
           child = new this.$$ChildScope();
         }
@@ -231,13 +241,9 @@ function $RootScopeProvider() {
         // prototypically. In all other cases, this property needs to be set
         // when the parent scope is destroyed.
         // The listener needs to be added after the parent is set
-        if (isolate || parent != this) child.$on('$destroy', destroyChild);
+        if (isolate || parent != this) child.$on('$destroy', destroyChildScope);
 
         return child;
-
-        function destroyChild() {
-          child.$$destroyed = true;
-        }
       },
 
       /**