fix($parse): make sure ES6 object computed properties are watched

Add the missing watches for ES6 object computed properties which were
implemented in #14407.

Closes #15678

src/ng/parse.js

@@ -717,6 +717,13 @@ function findConstantAndWatchExpressions(ast, $filter) {
       if (!property.value.constant) {
         argsToWatch.push.apply(argsToWatch, property.value.toWatch);
       }
+      if (property.computed) {
+        findConstantAndWatchExpressions(property.key, $filter);
+        if (!property.key.constant) {
+          argsToWatch.push.apply(argsToWatch, property.key.toWatch);
+        }
+      }
+
     });
     ast.constant = allConstants;
     ast.toWatch = argsToWatch;

test/ng/parseSpec.js

@@ -3119,6 +3119,39 @@ describe('parser', function() {
           expect(objB.value).toBe(scope.input);
         }));
 
+        it('should watch ES6 object computed property changes', function() {
+          var count = 0;
+          var values = [];
+
+          scope.$watch('{[a]: true}', function(val) {
+            count++;
+            values.push(val);
+          }, true);
+
+          scope.$digest();
+          expect(count).toBe(1);
+          expect(values[0]).toEqual({'undefined': true});
+
+          scope.$digest();
+          expect(count).toBe(1);
+          expect(values[0]).toEqual({'undefined': true});
+
+          scope.a = true;
+          scope.$digest();
+          expect(count).toBe(2);
+          expect(values[1]).toEqual({'true': true});
+
+          scope.a = 'abc';
+          scope.$digest();
+          expect(count).toBe(3);
+          expect(values[2]).toEqual({'abc': true});
+
+          scope.a = undefined;
+          scope.$digest();
+          expect(count).toBe(4);
+          expect(values[3]).toEqual({'undefined': true});
+        });
+
         it('should support watching literals', inject(function($parse) {
           var lastVal = NaN;
           var callCount = 0;