feat(js size): Add a default @MirrorsUsed to Angular.

Closes dart-archive#409, dart-archive#237

demo/todo/web/main.dart

@@ -5,6 +5,12 @@ import 'todo.dart';
 
 import 'dart:html';
 
+// Everything in this library should be preserved by MirrorsUsed
+@MirrorsUsed(
+    targets: const['todo'],
+    override: '*')
+import 'dart:mirrors';
+
 main() {
 
   print(window.location.search);

demo/todo/web/todo.dart

@@ -2,6 +2,7 @@ library todo;
 
 import 'package:angular/angular.dart';
 
+
 class Item {
   String text;
   bool done;

lib/angular.dart

@@ -15,6 +15,42 @@ import 'dart:js' as js;
 import 'package:di/di.dart';
 import 'package:di/dynamic_injector.dart';
 
+/**
+* This @MirrorsUsed annotation is doing two things:
+*   - setting "override: *", which will cause any library that is not tagged
+*     with @MirrorsUsed to be potentially shaken out of the production binary.
+*   - setting targets.  All classes inside of Angular will be preserved, as
+*     well as any class tagged with the annotations listed in metaTargets.
+*
+* If you are writing code accessed from Angular expressions, you must include
+* your own @MirrorsUsed annotation or ensure that everything is tagged with
+* the Ng annotations.
+*
+* This is a short-term fix until we implement a transformer-based solution
+* which does not rely on mirrors.
+*/
+@MirrorsUsed(targets: const[
+    'angular',
+    'angular.core',
+    'angular.core.dom',
+    'angular.filter',
+    'angular.perf',
+    'angular.directive',
+    'angular.routing',
+    'angular.core.parser.dynamic_parser',
+    'angular.core.parser.lexer',
+    'perf_api',
+    'List',
+    'NodeTreeSanitizer',
+],
+metaTargets: const[
+  'NgInjectableService',
+  'NgDirective',
+  'NgController',
+  'NgComponent'
+])
+import 'dart:mirrors';
+
 import 'package:angular/core/module.dart';
 import 'package:angular/core_dom/module.dart';
 import 'package:angular/directive/module.dart';

lib/playback/playback_http.dart

@@ -5,10 +5,12 @@ import 'dart:convert' show JSON;
 import 'dart:html';
 
 import 'package:angular/core_dom/module.dart';
+import 'package:angular/core/service.dart';
 import 'package:angular/mock/module.dart' as mock;
 
 import 'playback_data.dart' as playback_data;
 
+@NgInjectableService()
 class PlaybackHttpBackendConfig {
   requestKey(String url,
                  {String method, bool withCredentials, String responseType,