Make the HTTP MockClient work with GET requests.

pkg/http/lib/src/utils.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.
 
 library utils;
 
 import 'dart:crypto';
 import 'dart:io';
 import 'dart:isolate';
 import 'dart:scalarlist';
@@ skipping 115 matching lines @@
   if (input is Uint8List) return input;
   if (input is ByteArrayViewable) input = input.asByteArray();
   if (input is ByteArray) return new Uint8List.view(input);
   var output = new Uint8List(input.length);
   output.setRange(0, input.length, input);
   return output;
 }
 
 /// Buffers all input from an InputStream and returns it as a future.
 Future<List<int>> consumeInputStream(InputStream stream) {
+  if (stream.closed) return new Future<List<int>>.immediate(<int>[]);
+
   var completer = new Completer<List<int>>();
   /// TODO(nweiz): use BufferList when issue 6409 is fixed
   var buffer = <int>[];
   stream.onClosed = () => completer.complete(buffer);
   stream.onData = () => buffer.addAll(stream.read());
   stream.onError = completer.completeException;
   return completer.future;
 }
 
 /// Takes all input from [source] and writes it to [sink], then closes [sink].
@@ skipping 53 matching lines @@
 
 /// Configures [future] so that its result (success or exception) is passed on
 /// to [completer].
 void chainToCompleter(Future future, Completer completer) {
   future.handleException((e) {
     completer.completeException(e);
     return true;
   });
   future.then(completer.complete);
 }