fix(change-detection): correctly detect isMethod in StaticFieldGetter…

…Factory

lib/change_detection/dirty_checking_change_detector_static.dart

@@ -12,7 +12,10 @@ class StaticFieldGetterFactory implements FieldGetterFactory {
     // We need to know if we are referring to method or field which is a
     // function. We can find out by calling it twice and seeing if we get
     // the same value. Methods create a new closure each time.
-    return !identical(getter(object, name), getter(object, name));
+    FieldGetter getterFn = getter(object, name);
+    dynamic property = getterFn(object);
+    return (property is Function) &&
+           (!identical(property, getterFn(object)));
   }
 
   FieldGetter getter(Object object, String name) {

test/change_detection/dirty_checking_change_detector_spec.dart

@@ -13,13 +13,22 @@ void main() {
     FieldGetterFactory getterFactory = new StaticFieldGetterFactory({
         "first": (o) => o.first,
         "age": (o) => o.age,
-        "last": (o) => o.last
+        "last": (o) => o.last,
+        "toString": (o) => o.toString
     });
 
     beforeEach(() {
       detector = new DirtyCheckingChangeDetector<String>(getterFactory);
     });
 
+    describe('StaticFieldGetterFactory', () {
+      it('should detect methods', () {
+        var obj = new _User();
+        expect(getterFactory.isMethod(obj, 'toString')).toEqual(true);
+        expect(getterFactory.isMethod(obj, 'age')).toEqual(false);
+      });
+    });
+
     describe('object field', () {
       it('should detect nothing', () {
         var changes = detector.collectChanges();