Remove string concatenation with + from all Dart files in tools directory.

tools/testing/dart/test_runner.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.
 
 /**
  * Classes and methods for executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 527 matching lines @@
     if (allowRetries && testCase.usesWebDriver
         && testCase.output.unexpectedOutput
         && testCase.dynamic.numRetries > 0) {
       // Selenium tests can be flaky. Try rerunning.
       testCase.output.requestRetry = true;
     }
     if (testCase.output.requestRetry) {
       testCase.output.requestRetry = false;
       this.timedOut = false;
       testCase.dynamic.numRetries--;
-      print("Potential flake. Re-running ${testCase.displayName} " +
+      print("Potential flake. Re-running ${testCase.displayName} "
           "(${testCase.dynamic.numRetries} attempt(s) remains)");
       this.start();
     } else {
       testCase.completed();
     }
   }
 
   /**
    * Process exit handler called at the end of every command. It internally
    * treats all but the last command as compilation steps. The last command is
@@ skipping 160 matching lines @@
     _stdoutDrained = false;
     _stderrDrained = false;
     _stdoutStream.onLine = _readStdout(_stdoutStream, _testStdout);
     _stderrStream.onLine = _readStderr(_stderrStream, _testStderr);
     _timer = new Timer(testCase.timeout * 1000, _timeoutHandler);
     var line = _createArgumentsLine(testCase.batchTestArguments);
     _process.stdin.write(line.charCodes());
   }
 
   String _createArgumentsLine(List<String> arguments) {
-    return Strings.join(arguments, ' ') + '\n';
+    return Strings.join(arguments, ' ').concat('\n');
   }
 
   void _testCompleted() {
     var test = _currentTest;
     _currentTest = null;
     test.completed();
   }
 
   int _reportResult(String output) {
     _stdoutDrained = true;
@@ skipping 290 matching lines @@
 
   /**
    * For browser tests using Safari or Opera, we need to use the Selenium 1.0
    * Java server.
    */
   void _startSeleniumServer() {
     // Get the absolute path to the Selenium jar.
     String filePath = new Options().script;
     String pathSep = Platform.pathSeparator;
     int index = filePath.lastIndexOf(pathSep);
-    filePath = filePath.substring(0, index) + '${pathSep}testing${pathSep}';
+    filePath = '${filePath.substring(0, index)}${pathSep}testing${pathSep}';
     var lister = new Directory(filePath).list();
     lister.onFile = (String file) {
       if (const RegExp(@"selenium-server-standalone-.*\.jar").hasMatch(file)
           && _seleniumServer == null) {
         _seleniumServer = Process.start('java', ['-jar', file]);
         _seleniumServer.onError = (e) {
           print("Error starting process:");
           print("  Command: java -jar $file");
           print("  Error: $e");
         };
@@ skipping 37 matching lines @@
       if (!runner.active) return runner;
     }
     throw new Exception('Unable to find inactive batch runner.');
   }
 
   void _tryRunTest() {
     _checkDone();
     if (_numProcesses < _maxProcesses && !_tests.isEmpty()) {
       TestCase test = _tests.removeFirst();
       if (_listTests) {
-        final String tab = '\t';
-        String outcomes =
-            Strings.join(new List.from(test.expectedOutcomes), ',');
-        print(test.displayName + tab + outcomes + tab + test.isNegative +
-              tab + Strings.join(test.commands.last().arguments, tab));
+        var fields = [test.displayName,
+                      Strings.join(new List.from(test.expectedOutcomes), ','),
+                      test.isNegative];
+        fields.addAll(test.commands.last().arguments);
+        print(Strings.join(fields, '\t'));
         return;
       }
       if (test.usesWebDriver && _needsSelenium && !_isSeleniumAvailable) {
         // The server is not ready to run Selenium tests. Put the test back in
         // the queue.  Avoid spin-polling by using a timeout.
         _tests.add(test);
         new Timer(1000, (timer) {_tryRunTest();});  // Don't lose a process.
         return;
       }
       if (_verbose) {
@@ skipping 23 matching lines @@
         // the developer doesn't waste his or her time trying to fix a bunch of
         // tests that appear to be broken but were actually just flakes that
         // didn't get retried because there had already been one failure.
         bool allowRetry = _MAX_FAILED_NO_RETRY > _progress.numFailedTests;
         new RunningProcess(test, allowRetry, this).start();
       }
       _numProcesses++;
     }
   }
 }