feat(async): added PromiseWrapper.wrap

modules/angular2/src/facade/async.dart

@@ -19,6 +19,10 @@ class PromiseWrapper {
     return promise.then(success, onError: onError);
   }
 
+  static Future wrap(Function fn) {
+    return new Future(fn);
+  }
+  
   // Note: We can't rename this method to `catch`, as this is not a valid
   // method name in Dart.
   static Future catchError(Future promise, Function onError) {

modules/angular2/src/facade/async.ts

@@ -28,6 +28,16 @@ export class PromiseWrapper {
     return promise.then(success, rejection);
   }
 
+  static wrap<T>(computation: () => T): Promise<T> {
+    return new Promise((res, rej) => {
+      try {
+        res(computation());
+      } catch (e) {
+        rej(e);
+      }
+    });
+  }
+
   static completer() {
     var resolve;
     var reject;