fix(scope): check on the listeners methods to handle destroyed scopes

Add several checks on the methods that handle listeners so they are
able to handle destroyed scopes that now do not have the references
to the `$$listeners` and `$$listenersCount` when destroyed

Closes angular#6897

src/ng/rootScope.js

@@ -751,6 +751,7 @@ function $RootScopeProvider(){
         }
         // recreate the $$destroyed flag
         this.$$destroyed = true;
+
       },
 
       /**
@@ -921,6 +922,7 @@ function $RootScopeProvider(){
        * @returns {function()} Returns a deregistration function for this listener.
        */
       $on: function(name, listener) {
+        if (this.$$destroyed) return noop;
         var namedListeners = this.$$listeners[name];
         if (!namedListeners) {
           this.$$listeners[name] = namedListeners = [];
@@ -933,10 +935,11 @@ function $RootScopeProvider(){
             current.$$listenerCount[name] = 0;
           }
           current.$$listenerCount[name]++;
-        } while ((current = current.$parent));
+        } while ((current = current.$parent) && !current.$$destroyed);
 
         var self = this;
         return function() {
+          if (self.$$destroyed) return;
           namedListeners[indexOf(namedListeners, listener)] = null;
           decrementListenerCount(self, 1, name);
         };
@@ -982,7 +985,7 @@ function $RootScopeProvider(){
             listenerArgs = concat([event], arguments, 1),
             i, length;
 
-        do {
+        while (scope && !scope.$$destroyed) {
           namedListeners = scope.$$listeners[name] || empty;
           event.currentScope = scope;
           for (i=0, length=namedListeners.length; i<length; i++) {
@@ -1005,7 +1008,7 @@ function $RootScopeProvider(){
           if (stopPropagation) return event;
           //traverse upwards
           scope = scope.$parent;
-        } while (scope);
+        }
 
         return event;
       },
@@ -1113,7 +1116,7 @@ function $RootScopeProvider(){
         if (current.$$listenerCount[name] === 0) {
           delete current.$$listenerCount[name];
         }
-      } while ((current = current.$parent));
+      } while ((current = current.$parent) && !current.$$destroyed);
     }
 
     /**

test/ng/rootScopeSpec.js

@@ -874,6 +874,64 @@ describe('Scope', function() {
       $rootScope.$broadcast(EVENT);
       expect(spy.callCount).toBe(1);
     }));
+
+    it('should not throw when trying to listen to an event on a child scope of an already destroyed scope', inject(function($rootScope) {
+      var parent = $rootScope.$new(),
+        child = parent.$new();
+
+      parent.$destroy();
+      expect(function() {
+        var fn = child.$on('someEvent', angular.noop);
+        fn();
+      }).not.toThrow();
+    }));
+
+    it('should not throw when deregistering a listener on a child scope of an already destroyed scope', inject(function($rootScope) {
+      var parent = $rootScope.$new(),
+        child = parent.$new(),
+        fn = child.$on('someEvent', angular.noop);
+
+      parent.$destroy();
+      expect(function() { fn(); }).not.toThrow();
+    }));
+
+    it('should not throw when trying to destroy a child insolated scope of an already destroyed scope', inject(function($rootScope) {
+      var parent = $rootScope.$new(),
+        child = parent.$new(true),
+        fn = child.$on('someEvent', angular.noop);
+
+      parent.$destroy();
+      expect(function() { child.$destroy(); }).not.toThrow();
+    }));
+
+    it('should not throw when trying to listen to an event on an insolated child scope of an already destroyed scope', inject(function($rootScope) {
+      var parent = $rootScope.$new(),
+        child = parent.$new(true);
+
+      parent.$destroy();
+      expect(function() {
+        var fn = child.$on('someEvent', angular.noop);
+        fn();
+      }).not.toThrow();
+    }));
+
+    it('should not throw when deregistering a listener on an insolated child scope of an already destroyed scope', inject(function($rootScope) {
+      var parent = $rootScope.$new(),
+        child = parent.$new(true),
+        fn = child.$on('someEvent', angular.noop);
+
+      parent.$destroy();
+      expect(function() { fn(); }).not.toThrow();
+    }));
+
+    it('should not throw when trying to emit from an insolated child scope of a destroyed scope', inject(function($rootScope) {
+      var parent = $rootScope.$new(),
+        child = parent.$new(true),
+        fn = child.$on('someEvent', angular.noop);
+
+      parent.$destroy();
+      expect(function() { child.$emit('someEvent'); }).not.toThrow();
+    }));
   });