chore(analytics): Build hello_world, check constraints

Create gulp targets to build `hello_world` and check its gzipped size
against size constraints.

See #5312, #5314

modules_dart/payload/hello_world/web/index.dart

@@ -0,0 +1,68 @@
+library hello_world.index;
+
+import "package:angular2/bootstrap.dart" show bootstrap;
+import "package:angular2/core.dart"
+    show ElementRef, Component, Directive, Injectable;
+import "package:angular2/render.dart" show Renderer;
+
+main() {
+  // Bootstrapping only requires specifying a root component.
+
+  // The boundary between the Angular application and the rest of the page is
+
+  // the shadowDom of this root component.
+
+  // The selector of the component passed in is used to find where to insert the
+
+  // application.
+
+  // You can use the light dom of the <hello-app> tag as temporary content (for
+
+  // example 'Loading...') before the application is ready.
+  bootstrap(HelloCmp);
+}
+
+// A service available to the Injector, used by the HelloCmp component.
+@Injectable()
+class GreetingService {
+  String greeting = "hello";
+}
+// Directives are light-weight. They don't allow new
+
+// expression contexts (use @Component for those needs).
+@Directive(selector: "[red]")
+class RedDec {
+  // ElementRef is always injectable and it wraps the element on which the
+
+  // directive was found by the compiler.
+  RedDec(ElementRef el, Renderer renderer) {
+    renderer.setElementStyle(el, "color", "red");
+  }
+}
+// Angular 2.0 supports 2 basic types of directives:
+
+// - Component - the basic building blocks of Angular 2.0 apps. Backed by
+
+//   ShadowDom.(http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom/)
+
+// - Directive - add behavior to existing elements.
+
+// @Component is AtScript syntax to annotate the HelloCmp class as an Angular
+
+// 2.0 component.
+@Component(
+    selector: "hello-app",
+    viewProviders: const [GreetingService],
+    template:
+        '''<div class="greeting">{{greeting}} <span red>world</span>!</div>
+           <button class="changeButton" (click)="changeGreeting()">change greeting</button>''',
+    directives: const [RedDec])
+class HelloCmp {
+  String greeting;
+  HelloCmp(GreetingService service) {
+    this.greeting = service.greeting;
+  }
+  void changeGreeting() {
+    this.greeting = "howdy";
+  }
+}