add generic method comments to a few SDK methods

sdk/lib/async/future.dart

Index: sdk/lib/async/future.dart
diff --git a/sdk/lib/async/future.dart b/sdk/lib/async/future.dart
index 30016f7acc8eabf180d49f0ba49f0f103a000be8..bcc20192b1471ae59e7604f04965b760dcdbbea6 100644
--- a/sdk/lib/async/future.dart
+++ b/sdk/lib/async/future.dart
@@ -254,9 +254,9 @@ abstract class Future<T> {
    * The call to `cleanUp` should not throw. If it does, the error will be an
    * uncaught asynchronous error.
    */
-  static Future<List> wait(Iterable<Future> futures,
+  static Future<List/*<T>*/> wait/*<T>*/(Iterable<Future/*<T>*/> futures,
                            {bool eagerError: false,
-                            void cleanUp(successValue)}) {
+                            void cleanUp(/*=T*/ successValue)}) {
     final _Future<List> result = new _Future<List>();
     List values;  // Collects the values. Set to null on error.
     int remaining = 0;  // How many futures are we waiting for.
@@ -407,7 +407,7 @@ abstract class Future<T> {
    * with a `test` parameter, instead of handling both value and error in a
    * single [then] call.
    */
-  Future then(onValue(T value), { Function onError });
+  Future/*<S>*/ then/*<S>*/(/*=S*/ onValue(T value), { Function onError });
 
   /**
    * Handles errors emitted by this [Future].