fix(closure): don't throw from top-level

workaround for http://b/27151095

modules/angular2/src/core/util/decorators.ts

@@ -238,9 +238,13 @@ export function Class(clsDef: ClassDefinition): ConcreteType {
 }
 
 var Reflect = global.Reflect;
+// Throw statement at top-level is disallowed by closure compiler in ES6 input.
+// Wrap in an IIFE as a work-around.
+(function checkReflect() {
   if (!(Reflect && Reflect.getMetadata)) {
     throw 'reflect-metadata shim is required when using class decorators';
   }
+})();
 
 export function makeDecorator(
     annotationCls, chainFn: (fn: Function) => void = null): (...args: any[]) => (cls: any) => any {