feat(dart): Add a dev-mode check for undeclared lifecycle interfaces

Add a check in `ReflectionCapabilities#interfaces` which determines if
the passed-in type implements a Lifecycle Interface but does not declare
that it does so.

See https://goo.gl/b07Kii for details.

Closes #6849

modules/angular2/test/core/reflection/reflector_spec.ts

@@ -7,6 +7,7 @@ import {
   beforeEach,
   browserDetection
 } from 'angular2/testing_internal';
+import {OnInit} from 'angular2/core';
 import {Reflector, ReflectionInfo} from 'angular2/src/core/reflection/reflection';
 import {ReflectionCapabilities} from 'angular2/src/core/reflection/reflection_capabilities';
 import {
@@ -65,6 +66,19 @@ class SuperClassImplementingInterface implements Interface2 {}
 
 class ClassImplementingInterface extends SuperClassImplementingInterface implements Interface {}
 
+// Classes used to test our runtime check for classes that implement lifecycle interfaces but do not
+// declare them.
+// See https://github.com/angular/angular/pull/6879 and https://goo.gl/b07Kii for details.
+class ClassDoesNotDeclareOnInit {
+  ngOnInit() {}
+}
+
+class SuperClassImplementingOnInit implements OnInit {
+  ngOnInit() {}
+}
+
+class SubClassDoesNotDeclareOnInit extends SuperClassImplementingOnInit {}
+
 export function main() {
   describe('Reflector', () => {
     var reflector;
@@ -214,6 +228,14 @@ export function main() {
           var p = reflector.interfaces(ClassWithDecorators);
           expect(p).toEqual([]);
         });
+
+        it("should throw for undeclared lifecycle interfaces",
+           () => { expect(() => reflector.interfaces(ClassDoesNotDeclareOnInit)).toThrowError(); });
+
+        it("should throw for class inheriting a lifecycle impl and not declaring the interface",
+           () => {
+             expect(() => reflector.interfaces(SubClassDoesNotDeclareOnInit)).toThrowError();
+           });
       });
     }