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

tools/testing/dart/test_progress.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.
 
 #library("test_progress");
 
 #import("dart:io");
 #import("dart:builtin");
 #import("test_runner.dart");
 #import("test_suite.dart");
@@ skipping 234 matching lines @@
   CompactProgressIndicator(Date startTime, bool printTiming)
       : super(startTime, printTiming);
 
   void _printProgress() {
     var percent = ((_completedTests() / _foundTests) * 100).toInt().toString();
     var progressPadded = _pad(_allTestsKnown ? percent : '--', 3);
     var passedPadded = _pad(_passedTests.toString(), 5);
     var failedPadded = _pad(_failedTests.toString(), 5);
     Duration d = (new Date.now()).difference(_startTime);
     var progressLine =
-        '\r[${_timeString(d)} | $progressPadded% | ' +
+        '\r[${_timeString(d)} | $progressPadded% | '
         '+$passedPadded | -$failedPadded]';
     stdout.write(progressLine.charCodes());
   }
 }
 
 
 class ColorProgressIndicator extends CompactIndicator {
   ColorProgressIndicator(Date startTime, bool printTiming)
       : super(startTime, printTiming);
 
@@ skipping 85 matching lines @@
     var status = 'pass';
     if (test.output.unexpectedOutput) {
       status = 'fail';
     }
     var percent = ((_completedTests() / _foundTests) * 100).toInt().toString();
     print('Done ${test.configurationString} ${test.displayName}: $status');
     print('@@@STEP_CLEAR@@@');
     print('@@@STEP_TEXT@ $percent% +$_passedTests -$_failedTests @@@');
   }
 }