Added support for skipping redundant dart2js compilations.

tools/testing/dart/test_suite.dart

Index: tools/testing/dart/test_suite.dart
diff --git a/tools/testing/dart/test_suite.dart b/tools/testing/dart/test_suite.dart
index 84fd882b2df7fd3a2a5c5304f2ff6009ee9d9b3e..8d4300df016804a864e8646be100da2e410e3560 100644
--- a/tools/testing/dart/test_suite.dart
+++ b/tools/testing/dart/test_suite.dart
@@ -20,6 +20,7 @@
 #import("test_runner.dart");
 #import("multitest.dart");
 #import("drt_updater.dart");
+#import("dart:uri");
 
 #source("browser_test.dart");
 
@@ -443,6 +444,19 @@ class StandardTestSuite extends TestSuite {
         recursive: true);
   }
 
+  Collection<Uri> get dart2JsBootstrapDependencies {
+    if (!useDart2JsFromSdk) return [];
+    
+    var snapshotPath = TestUtils.absolutePath(new Path(buildDir).join(
+        new Path('dart-sdk/lib/_internal/compiler/'
+                 'implementation/dart2js.dart.snapshot'))).toString();
+    return [new Uri.fromComponents(scheme: 'file', path: snapshotPath)];
+  }
+
+  bool get useDart2JsFromSdk {
+    return configuration['use_sdk'];
+  }
+
   /**
    * The default implementation assumes a file is a test if
    * it ends in "Test.dart".
@@ -698,7 +712,12 @@ class StandardTestSuite extends TestSuite {
       args = new List.from(args);
       String tempDir = createOutputDirectory(info.filePath, '');
       args.add('--out=$tempDir/out.js');
-      List<Command> commands = <Command>[new Command(dartShellFileName, args)];
+      List<Command> commands = 
+          <Command>[new Dart2JsCommand("$tempDir/out.js",
+                                       !useDart2JsFromSdk,
+                                       dart2JsBootstrapDependencies,
+                                       dartShellFileName,
+                                       args)];
       if (info.hasCompileError) {
         // Do not attempt to run the compiled result. A compilation
         // error should be reported by the compilation command.
@@ -999,6 +1018,13 @@ class StandardTestSuite extends TestSuite {
       args.insertRange(0, 1, executable);
       executable = dartShellFileName;
     }
+    if (configuration['compiler'] == 'dart2js') {
+      return new Dart2JsCommand(outputFile,
+                                !useDart2JsFromSdk, 
+                                dart2JsBootstrapDependencies,
+                                dartShellFileName,
+                                args);
+    }
     return new Command(executable, args);
   }
 
@@ -1460,6 +1486,31 @@ class JUnitTestSuite extends TestSuite {
   }
 }
 
+class LastModifiedCache {
+  Map<String, Date> _cache = <String, Date>{};
+
+  /**
+   * Returns the last modified date of the given [uri].
+   * 
+   * The return value will be cached for future queries. If [uri] is a local
+   * file, it's last modified [Date] will be returned. If the file does not
+   * exist, null will be returned instead.
+   * In case [uri] is not a local file, this method will always return
+   * the current date.
+   */
+  Date getLastModified(Uri uri) {
+    if (uri.scheme == "file") {
+      if (_cache.containsKey(uri.path)) {
+        return _cache[uri.path];
+      }
+      var file = new File(uri.path);
+      _cache[uri.path] = file.existsSync() ? file.lastModifiedSync() : null;
+      return _cache[uri.path];
+    }
+    return new Date.now();
+  }
+}
+
 class TestUtils {
   /**
    * The libraries in this directory relies on finding various files
@@ -1468,7 +1519,8 @@ class TestUtils {
    * script must set this to '.../dart/tools/test.dart'.
    */
   static String testScriptPath = new Options().script;
-
+  static LastModifiedCache lastModifiedCache = new LastModifiedCache();
+  static Path currentWorkingDirectory = new Path(new Directory.current().path);
   /**
    * Creates a directory using a [relativePath] to an existing
    * [base] directory if that [relativePath] does not already exist.
@@ -1516,6 +1568,13 @@ class TestUtils {
     }
   }
 
+  static Path absolutePath(Path path) {
+    if (!path.isAbsolute) {
+      return currentWorkingDirectory.join(path);
+    }
+    return path;
+  }
+
   static String outputDir(Map configuration) {
     var result = '';
     var system = configuration['system'];