Add optional writeAll separator argument.

sdk/lib/io/io_sink.dart

 // Copyright (c) 2013, 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.io;
 
 /**
  * Helper class to wrap a [StreamConsumer<List<int>, T>] and provide
  * utility functions for writing to the StreamConsumer directly. The
  * [IOSink] buffers the input given by [write], [writeAll], [writeln],
@@ skipping 76 matching lines @@
     } else {
       string = obj.toString();
       if (string is! String) {
         throw new ArgumentError('toString() did not return a string');
       }
     }
     if (string.isEmpty) return;
     writeBytes(_encodeString(string, _encoding));
   }
 
-  void writeAll(Iterable objects) {
-    for (Object obj in objects) write(obj);
+  void writeAll(Iterable objects, [String separator = ""]) {
+    bool isFirst = true;
+    for (Object obj in objects) {
+      if (isFirst) {
+        isFirst = false;
+      } else {
+        if (separator != "") write(separator);
+      }
+      write(obj);
+    }
   }
 
   void writeln([Object obj = ""]) {
     write(obj);
     write("\n");
   }
 
   void writeCharCode(int charCode) {
     write(new String.fromCharCode(charCode));
   }
@@ skipping 116 matching lines @@
         },
         onError: _controller.addError);
     if (_paused) _pause();
     if (unbind) {
       return _writeStreamCompleter.future;
     } else {
       return _pipeFuture;
     }
   }
 }