Rename String.concat to operator+.

runtime/lib/string_base.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.
 
 /**
  * [_StringBase] contains common methods used by concrete String
  * implementations, e.g., _OneByteString.
  */
 class _StringBase {
 
@@ skipping 21 matching lines @@
   String operator [](int index) native "String_charAt";
 
   int codeUnitAt(int index) native "String_codeUnitAt";
 
   int get length native "String_getLength";
 
   bool get isEmpty {
     return this.length == 0;
   }
 
-  String concat(String other) native "String_concat";
+  String operator +(String other) native "String_concat";
+
+  String concat(String other) => this + other;
 
   String toString() {
     return this;
   }
 
   bool operator ==(Object other) {
     if (identical(this, other)) {
       return true;
     }
     if ((other is !String) ||
@@ skipping 544 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int start;
   final String str;
   final String pattern;
 }