Clean up test_runner Command subclass hash/equality.

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
@@ skipping 151 matching lines @@
         ..addAll(vmOptions)
         ..addAll(sharedOptions)
         ..addAll(originalArguments);
   }
 }
 
 /// Common configuration for dart2js-based tools, such as, dart2js and
 /// dart2dart.
 class Dart2xCompilerConfiguration extends CompilerConfiguration {
   final String moniker;
+  static Map<String, List<Uri>> _bootstrapDependenciesCache =
+      new Map<String, List<Uri>>();
 
   Dart2xCompilerConfiguration(
       this.moniker,
       {bool isDebug,
       bool isChecked,
       bool isHostChecked,
       bool useSdk})
       : super._subclass(
           isDebug: isDebug, isChecked: isChecked,
           isHostChecked: isHostChecked, useSdk: useSdk);
@@ skipping 25 matching lines @@
 
     return commandBuilder.getCompilationCommand(
         moniker, outputFileName, !useSdk,
         bootstrapDependencies(buildDir),
         computeCompilerPath(buildDir),
         arguments, environmentOverrides);
   }
 
   List<Uri> bootstrapDependencies(String buildDir) {
     if (!useSdk) return const <Uri>[];
-
-    Uri absoluteBuildDir = Uri.base.resolveUri(nativeDirectoryToUri(buildDir));
-    return [absoluteBuildDir.resolve(
-          'dart-sdk/bin/snapshots/dart2js.dart.snapshot')];
+    return _bootstrapDependenciesCache.putIfAbsent(buildDir, () =>
+      [Uri.base.resolveUri(nativeDirectoryToUri(buildDir))
+               .resolve('dart-sdk/bin/snapshots/dart2js.dart.snapshot')]);
   }
 }
 
 /// Configuration for dart2js compiler.
 class Dart2jsCompilerConfiguration extends Dart2xCompilerConfiguration {
   final bool isCsp;
   final List<String> extraDart2jsOptions;
 
   Dart2jsCompilerConfiguration({
       bool isDebug,
@@ skipping 155 matching lines @@
       bool isDebug,
       bool isChecked,
       bool isHostChecked,
       bool useSdk})
       : super(
           'dart2analyzer', isDebug: isDebug, isChecked: isChecked,
           isHostChecked: isHostChecked, useSdk: useSdk);
 
   String computeCompilerPath(String buildDir) => 'editor/tools/analyzer';
 }