Add wrapper shell script to invoke dartk with checked-in binary

tools/testing/dart/compiler_configuration.dart

 // Copyright (c) 2014, 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 compiler_configuration;
 
 import 'dart:io' show Platform;
 
 import 'runtime_configuration.dart' show RuntimeConfiguration;
 
@@ skipping 199 matching lines @@
   }
 }
 
 /// The "dartk" compiler.
 class DartKCompilerConfiguration extends CompilerConfiguration {
   DartKCompilerConfiguration({bool isHostChecked, bool useSdk})
       : super._subclass(isHostChecked: isHostChecked, useSdk: useSdk);
 
   @override
   String computeCompilerPath(String buildDir) {
-    return 'third_party/pkg/kernel/bin/dartk.dart';
+    return 'tools/dartk_wrappers/dartk$executableScriptSuffix';

[kustermann, 2016/11/18 16:32:39]

At some point we will add a tools/dartk_wrappers/dartk.bat file.

   }
 
   CompilationCommand computeCompilationCommand(
       String outputFileName,
       String buildDir,
       CommandBuilder commandBuilder,
       List arguments,
       Map<String, String> environmentOverrides) {
     var extraArguments = [
       '--sdk',
@@ skipping 597 matching lines @@
       RuntimeConfiguration runtimeConfiguration,
       String buildDir,
       TestInformation info,
       List<String> vmOptions,
       List<String> sharedOptions,
       List<String> originalArguments,
       CommandArtifact artifact) {
     return <String>[];
   }
 }