Automatically append ".js" on spawnUri if we are running in JavaScript.

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 1052 matching lines @@
       if (compiler != 'none') {
         commands.add(_compileCommand(
             dartWrapperFilename, compiledDartWrapperFilename,
             compiler, tempDir, vmOptions, optionsFromFile));
       }
 
       // some tests require compiling multiple input scripts.
       List<String> otherScripts = optionsFromFile['otherScripts'];
       for (String name in otherScripts) {
         Path namePath = new Path(name);
-        String baseName = namePath.filenameWithoutExtension;
+        String fileName = namePath.filename;
         Path fromPath = filePath.directoryPath.join(namePath);
         if (compiler != 'none') {
           assert(namePath.extension == 'dart');
           commands.add(_compileCommand(
-              fromPath.toNativePath(), '$tempDir/$baseName.js',
+              fromPath.toNativePath(), '$tempDir/$fileName.js',
               compiler, tempDir, vmOptions, optionsFromFile));
         }
         if (compiler == 'none') {
           // For the tests that require multiple input scripts but are not
           // compiled, move the input scripts over with the script so they can
           // be accessed.
           String result = new File(fromPath.toNativePath()).readAsStringSync();
-          new File('$tempDir/$baseName.dart').writeAsStringSync(result);
+          new File('$tempDir/$fileName').writeAsStringSync(result);
         }
       }
 
 
       // Variables for browser multi-tests.
       List<String> subtestNames = info.optionsFromFile['subtestNames'];
       int subtestIndex = 0;
       // Construct the command that executes the browser test
       do {
         List<Command> commandSet = new List<Command>.from(commands);
@@ skipping 956 matching lines @@
  * $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
  * $compileErrorSkip tests are skipped on browsers due to compile-time error
 """;
     print(report);
    }
 }