Add a generic type to Future.forEach.

sdk/lib/async/future.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.async;
 
 /// A type representing values that are either `Future<T>` or `T`.
 ///
 /// This class declaration is a public stand-in for an internal
 /// future-or-value generic type. References to this class are resolved to the
@@ skipping 400 matching lines @@
    * Runs [f] for each element in [input] in order, moving to the next element
    * only when the [Future] returned by [f] completes. Returns a [Future] that
    * completes when all elements have been processed.
    *
    * The return values of all [Future]s are discarded. Any errors will cause the
    * iteration to stop and will be piped through the returned [Future].
    *
    * If [f] returns a non-[Future], iteration continues immediately. Otherwise
    * it waits for the returned [Future] to complete.
    */
-  static Future forEach(Iterable input, f(element)) {
-    Iterator iterator = input.iterator;
+  static Future forEach<T>(Iterable<T> input, f(T element)) {
+    var iterator = input.iterator;
     return doWhile(() {
       if (!iterator.moveNext()) return false;
       return new Future.sync(() => f(iterator.current)).then((_) => true);
     });
   }
 
   /**
    * Performs an async operation repeatedly until it returns `false`.
    *
    * The function [f] is called repeatedly while it returns either the [bool]
@@ skipping 387 matching lines @@
   if (replacement != null) {
     error = _nonNullError(replacement.error);
     stackTrace = replacement.stackTrace;
   }
   result._completeError(error, stackTrace);
 }
 
 /** Helper function that converts `null` to a [NullThrownError]. */
 Object _nonNullError(Object error) =>
   (error != null) ? error : new NullThrownError();