Better splitting of flag string.

tools/testing/dart/test_suite.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 enumerating and preparing tests.
  *
  * This library includes:
  *
  * - Creating tests by listing all the Dart files in certain directories,
@@ skipping 432 matching lines @@
       if (configuration['runtime'] == 'd8') {
         var d8 = TestUtils.d8FileName(configuration);
         commands.add(new Command(d8, ['$tempDir/out.js']));
       }
       return commands;
 
     case 'dart2dart':
       var compilerArguments = new List.from(args);
       var additionalFlags =
           configuration['additional-compiler-flags'].split(' ');
-      compilerArguments.addAll(additionalFlags);
+      for (final flag in additionalFlags) {
+        if (flag.isEmpty()) continue;
+        compilerArguments.add(flag);
+      }
       compilerArguments.add('--output-type=dart');
       String tempDir = createOutputDirectory(info.filePath, '');
       compilerArguments.add('--out=$tempDir/out.dart');
       List<Command> commands =
           <Command>[new Command(shellPath(), compilerArguments)];
       if (configuration['runtime'] == 'vm') {
         // TODO(antonm): support checked.
         var vmArguments = new List.from(vmOptions);
         vmArguments.addAll([
             '--ignore-unrecognized-flags', '$tempDir/out.dart']);
@@ skipping 946 matching lines @@
  * $noCrash tests are expected to be flaky but not crash
  * $pass tests are expected to pass
  * $failOk tests are expected to fail that we won't fix
  * $fail tests are expected to fail that we should fix
  * $crash tests are expected to crash that we should fix
  * $timeout tests are allowed to timeout
 """;
     print(report);
    }
 }