Fix various warnings from the analyzer.

sdk/lib/async/stream.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;
 
 // -------------------------------------------------------------------
 // Core Stream types
 // -------------------------------------------------------------------
 
@@ skipping 355 matching lines @@
    * Finds the least element in the stream.
    *
    * If the stream is empty, the result is [:null:].
    * Otherwise the result is a value from the stream that is not greater
    * than any other value from the stream (according to [compare], which must
    * be a [Comparator]).
    *
    * If [compare] is omitted, it defaults to [Comparable.compare].
    */
   Future<T> min([int compare(T a, T b)]) {
-    if (compare == null) compare = Comparable.compare;
+    if (compare == null) {
+      var defaultCompare = Comparable.compare;
+      compare = defaultCompare;
+    }
     _FutureImpl<T> future = new _FutureImpl<T>();
     StreamSubscription subscription;
     T min = null;
     subscription = this.listen(
       // TODO(ahe): Restore type when feature is implemented in dart2js
       // checked mode. http://dartbug.com/7733
       (/*T*/ value) {
         min = value;
         subscription.onData((T value) {
           _runUserCode(
@@ skipping 20 matching lines @@
    * Finds the largest element in the stream.
    *
    * If the stream is empty, the result is [:null:].
    * Otherwise the result is an value from the stream that is not smaller
    * than any other value from the stream (according to [compare], which must
    * be a [Comparator]).
    *
    * If [compare] is omitted, it defaults to [Comparable.compare].
    */
   Future<T> max([int compare(T a, T b)]) {
-    if (compare == null) compare = Comparable.compare;
+    if (compare == null)  {
+      var defaultCompare = Comparable.compare;
+      compare = defaultCompare;
+    }
     _FutureImpl<T> future = new _FutureImpl<T>();
     StreamSubscription subscription;
     T max = null;
     subscription = this.listen(
       // TODO(ahe): Restore type when feature is implemented in dart2js
       // checked mode. http://dartbug.com/7733
       (/*T*/ value) {
         max = value;
         subscription.onData((T value) {
           _runUserCode(
@@ skipping 697 matching lines @@
 }
 
 class _StreamOutputSinkWrapper<T> implements StreamSink<T> {
   _StreamOutputSink _sink;
   _StreamOutputSinkWrapper(this._sink);
 
   void add(T data) => _sink._sendData(data);
   void signalError(AsyncError error) => _sink._sendError(error);
   void close() => _sink._sendDone();
 }