Rename String.concat to operator+.

tests/standalone/io/stream_pipe_test.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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 library ServerTest;
 
@@ skipping 50 matching lines @@
   // Force test to timeout if one of the handlers is
   // not called.
   ReceivePort donePort = new ReceivePort();
   donePort.receive((message, ignore) { donePort.close(); });
 
   String srcFileName =
       getDataFilename("tests/standalone/io/readline_test1.dat");
   var srcStream = new File(srcFileName).openRead();
 
   var tempDir = new Directory('').createTempSync();
-  String dstFileName = tempDir.path.concat("/readline_test1.dat");
+  String dstFileName = tempDir.path + "/readline_test1.dat";
   new File(dstFileName).createSync();
   var output = new File(dstFileName).openWrite();
   srcStream.pipe(output).then((_) {
     bool result = compareFileContent(srcFileName, dstFileName);
     new File(dstFileName).deleteSync();
     tempDir.deleteSync();
     Expect.isTrue(result);
     donePort.toSendPort().send(null);
   });
 }
 
 
 // Test piping from one file to another and write additional data to
 // the output stream after piping finished.
 testFileToFilePipe2() {
   // Force test to timeout if one of the handlers is
   // not called.
   ReceivePort donePort = new ReceivePort();
   donePort.receive((message, ignore) { donePort.close(); });
 
   String srcFileName =
       getDataFilename("tests/standalone/io/readline_test1.dat");
   var srcFile = new File(srcFileName);
   var srcStream = srcFile.openRead();
 
   var tempDir = new Directory('').createTempSync();
-  var dstFileName = tempDir.path.concat("/readline_test1.dat");
+  var dstFileName = tempDir.path + "/readline_test1.dat";
   var dstFile = new File(dstFileName);
   dstFile.createSync();
   var output = dstFile.openWrite();
   output.writeStream(srcStream).then((_) {
     output.writeBytes([32]);
     output.close();
     output.done.then((_) {
       var src = srcFile.openSync();
       var dst = dstFile.openSync();
       var srcLength = src.lengthSync();
@@ skipping 22 matching lines @@
   // not called.
   ReceivePort donePort = new ReceivePort();
   donePort.receive((message, ignore) { donePort.close(); });
 
   String srcFileName =
       getDataFilename("tests/standalone/io/readline_test1.dat");
   var srcFile = new File(srcFileName);
   var srcStream = srcFile.openRead();
 
   var tempDir = new Directory('').createTempSync();
-  var dstFileName = tempDir.path.concat("/readline_test1.dat");
+  var dstFileName = tempDir.path + "/readline_test1.dat";
   var dstFile = new File(dstFileName);
   dstFile.createSync();
   var output = dstFile.openWrite();
   output.writeStream(srcStream).then((_) {
     var srcStream2 = srcFile.openRead();
     output.writeStream(srcStream2).then((_) {
       output.close();
       output.done.then((_) {
         var src = srcFile.openSync();
         var dst = dstFile.openSync();
@@ skipping 16 matching lines @@
     });
   });
 }
 
 
 main() {
   testFileToFilePipe1();
   testFileToFilePipe2();
   testFileToFilePipe3();
 }