feat(facade): add read/write access to global variables

modules/angular2/src/facade/js_interop.dart

@@ -0,0 +1,15 @@
+library angular2.src.facade.js_interop;
+
+import 'dart:js' as js;
+
+setGlobalVar(String name, value) {
+  js.context[name] = value;
+}
+
+getGlobalVar(String name) {
+  return js.context[name];
+}
+
+invokeJsFunction(js.JsFunction fn, self, args) {
+  return fn.apply(args, thisArg: self);
+}

modules/angular2/src/facade/js_interop.ts

@@ -0,0 +1,13 @@
+import {global} from './lang';
+
+export function setGlobalVar(name: string, value: any) {
+  global[name] = value;
+}
+
+export function getGlobalVar(name: string) {
+  return global[name];
+}
+
+export function invokeJsFunction(fn: Function, self: any, args: List<any>) {
+  return fn.apply(self, args);
+}