Fix build

runtime/bin/socket_stream.dart

 // Copyright (c) 2011, 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.
 
 class SocketInputStream implements InputStream {
   SocketInputStream(Socket socket) {
     _socket = socket;
   }
 
   List<int> read([int len]) {
@@ skipping 147 matching lines @@
       if (bytesWritten == len) return true;
     }
 
     // Place remaining data on the pending writes queue.
     int notWrittenOffset = offset + bytesWritten;
     if (copyBuffer) {
       List<int> newBuffer =
           buffer.getRange(notWrittenOffset, len - bytesWritten);
       _pendingWrites.add(newBuffer);
     } else {
-      assert(offset + len = buffer.length);
+      assert(offset + len == buffer.length);
       _pendingWrites.add(buffer, notWrittenOffset);
     }
   }
 
   void _writeHandler() {
     // Write as much buffered data to the socket as possible.
     while (!_pendingWrites.isEmpty()) {
       List<int> buffer = _pendingWrites.first;
       int offset = _pendingWrites.index;
       int bytesToWrite = buffer.length - offset;
@@ skipping 19 matching lines @@
     if (_streamErrorHandler != null) _streamErrorHandler();
   }
 
   Socket _socket;
   _BufferList2 _pendingWrites;
   var _noPendingWriteHandler;
   var _streamErrorHandler;
   bool _closing = false;
   bool _closed = false;
 }