Roll Observatory packages and add a roll script

packages/usage/tool/grind.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 usage.grind;
+
+import 'dart:io';
+
+import 'package:grinder/grinder.dart';
+
+final Directory BUILD_DIR = new Directory('build');
+final Directory BUILD_TEST_DIR = new Directory('build/test');
+
+void main(List<String> args) {
+  task('init', init);
+  task('build', build, ['init']);
+  task('clean', clean);
+
+  startGrinder(args);
+}
+
+/// Do any necessary build set up.
+void init(GrinderContext context) {
+  // Verify we're running in the project root.
+  if (!getDir('lib').existsSync() || !getFile('pubspec.yaml').existsSync()) {
+    context.fail('This script must be run from the project root.');
+  }
+
+  BUILD_TEST_DIR.createSync(recursive: true);
+}
+
+void build(GrinderContext context) {
+  // Compile `test/web_test.dart` to the `build/test` dir; measure its size.
+  File srcFile = new File('test/web_test.dart');
+  Dart2js.compile(context, srcFile, outDir: BUILD_TEST_DIR, minify: true);
+  File outFile = joinFile(BUILD_TEST_DIR, ['web_test.dart.js']);
+
+  context.log('${outFile.path} compiled to ${_printSize(outFile)}');
+}
+
+/// Delete all generated artifacts.
+void clean(GrinderContext context) {
+  // Delete the build/ dir.
+  deleteEntity(BUILD_DIR, context);
+}
+
+String _printSize(File file) => '${(file.lengthSync() + 1023) ~/ 1024}k';