dart2js implementation of StringBuffer.writeAll that optimizes better

sdk/lib/core/string_buffer.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.
 
 part of dart.core;
 
 /**
  * A class for concatenating strings efficiently.
  *
  * Allows for the incremental building of a string using write*() methods.
@@ skipping 19 matching lines @@
    * operation.
    */
   bool get isNotEmpty => !isEmpty;
 
   /// Adds the contents of [obj], converted to a string, to the buffer.
   external void write(Object obj);
 
   /// Adds the string representation of [charCode] to the buffer.
   external void writeCharCode(int charCode);
 
-  void writeAll(Iterable objects, [String separator = ""]) {
-    Iterator iterator = objects.iterator;
-    if (!iterator.moveNext()) return;
-    if (separator.isEmpty) {
-      do {
-        write(iterator.current);
-      } while (iterator.moveNext());
-    } else {
-      write(iterator.current);
-      while (iterator.moveNext()) {
-        write(separator);
-        write(iterator.current);
-      }
-    }
-  }
+  external void writeAll(Iterable objects, [String separator = ""]);
 
-  void writeln([Object obj = ""]) {
-    write(obj);
-    write("\n");
-  }
+  external void writeln([Object obj = ""]);
 
   /**
    * Clears the string buffer.
    */
   external void clear();
 
   /// Returns the contents of buffer as a concatenated string.
   external String toString();
 }