Add Future.timeout.

sdk/lib/async/future_impl.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;
 
 /** The onValue and onError handlers return either a value or a future */
 typedef dynamic _FutureOnValue<T>(T value);
 /** Test used by [Future.catchError] to handle skip some errors. */
 typedef bool _FutureErrorTest(var error);
@@ skipping 519 matching lines @@
         listener._setValue(listenerValueOrError);
       } else {
         listeners = listener._removeListeners();
         _AsyncError asyncError = listenerValueOrError;
         listener._setError(asyncError.error, asyncError.stackTrace);
       }
       // Prepare for next round.
       source = listener;
     }
   }
+
+  Future timeout(Duration timeLimit, [void onTimeout()]) {
+    if (_isComplete) return new _Future.immediate(this);
+    _Future result = new _Future();
+    Timer timer;
+    if (onTimeout == null) {
+      timer = new Timer(timeLimit, () {
+        result._completeError(new TimeoutException(timeLimit));
+      });
+    } else {
+      Zone zone = Zone.current;
+      onTimeout = zone.registerCallback(onTimeout);
+      timer = new Timer(timeLimit, () {
+        try {
+          result._complete(zone.run(onTimeout));
+        } catch (e, s) {
+          result._completeError(e, s);
+        }
+      });
+    }
+    this.then((T v) {
+      if (timer.isActive) {
+        timer.cancel();
+        result._complete(v);
+      }
+    }, onError: (e, s) {
+      if (timer.isActive) {
+        timer.cancel();
+        result._completeError(e, s);
+      }
+    });
+    return result;
+  }
 }