Add tools script to update homebrew, the MacOS SDK updating solution.

tools/apps/update_homebrew/bin/update_homebrew.dart

Index: tools/apps/update_homebrew/bin/update_homebrew.dart
diff --git a/tools/apps/update_homebrew/bin/update_homebrew.dart b/tools/apps/update_homebrew/bin/update_homebrew.dart
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+++ b/tools/apps/update_homebrew/bin/update_homebrew.dart
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+// 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 update_homebrew;
+
+import 'dart:io';
+import 'dart:convert';
+import 'dart:async';
+import 'package:http/http.dart' as http;
+import 'package:args/args.dart';
+import 'package:googleapis/storage/v1.dart' as storage;
+import 'package:googleapis/common/common.dart' show DownloadOptions, Media;
+
+String repository;  // The path to the temporary git checkout of dart-homebrew.
+Map gitEnvironment;  // Pass a wrapper script for SSH to git in the environment.
+
+Future<String> getHash256(String channel, int revision, String download) {
+  var client = new http.Client();
+  var api = new storage.StorageApi(client);
+  return
+      api.objects.get('dart-archive',
+                      'channels/$channel/release/$revision/$download.sha256sum',
+                       downloadOptions: DownloadOptions.FullMedia)
+      .then((Media media) => ASCII.decodeStream(media.stream))
+      .then((hashLine) => new RegExp('[0-9a-fA-F]*').stringMatch(hashLine))
+      .whenComplete(client.close);
+}
+
+Future<String> getVersion(String channel, int revision) {
+  var client = new http.Client();
+  var api = new storage.StorageApi(client);
+  return api.objects.get('dart-archive',
+                         'channels/$channel/release/$revision/VERSION',
+                         downloadOptions: DownloadOptions.FullMedia)
+      .then((Media media) => JSON.fuse(ASCII).decoder.bind(media.stream).first)
+      .then((versionObject) => versionObject['version'])
+      .whenComplete(client.close);
+}
+
+Future writeHomebrewInfo(String channel, int revision) {
+  final buffer = new StringBuffer();
+  final moduleName = (channel == 'dev') ? 'DartDev' : 'DartStable';
+  buffer.writeln('module $moduleName');
+  final files = {'SDK64': 'sdk/dartsdk-macos-x64-release.zip',
+                 'SDK32': 'sdk/dartsdk-macos-ia32-release.zip',
+                 'DARTIUM': 'dartium/dartium-macos-ia32-release.zip'};
+  return Future.forEach(files.keys, (key) {
+    return getHash256(channel, revision, files[key]).then((hash) {
+      final file = "channels/$channel/release/$revision/${files[key]}";
+      buffer.writeln('  ${key}_FILE = "$file"');
+      buffer.writeln('  ${key}_HASH = "$hash"');
+    })
+  })
+    .then((_) => getVersion(channel, revision))
+    .then((version) {
+      buffer.writeln('  VERSION = "$version"');
+      buffer.writeln('end');
+      return (new File('$repository/data/${channel}_info.rb').openWrite()
+        ..write(buffer))
+        .close();
+    });
+}
+
+Future runGit(List<String> args) {
+  print("git ${args.join(' ')}");
+  return Process.run('git', args, workingDirectory: repository,
+                     environment: gitEnvironment)
+      .then((result) {
+        print(result.stdout);
+        print(result.stderr);
+      });
+}
+
+main(args) {
+  final parser = new ArgParser()
+      ..addOption('revision', abbr: 'r')
+      ..addOption('channel', abbr: 'c', allowed: ['dev', 'stable'])
+      ..addOption('key', abbr: 'k');
+  final options = parser.parse(args);
+  final revision = options['revision'];
+  final channel = options['channel'];
+  final sshWrapper = Platform.script.resolve('ssh_with_key').toFilePath();
+  gitEnvironment = {'GIT_SSH': sshWrapper,
+                    'SSH_KEY_PATH': options['key']};
+
+  Directory.systemTemp.createTemp('update_homebrew')
+      .then((tempDir) {
+        repository = tempDir.path;
+      })
+      .then((_) => runGit(
+          ['clone', 'git@github.com:dart-lang/homebrew-dart.git', '.']))
+      .then((_) => writeHomebrewInfo(channel, revision))
+      .then((_) => runGit(['add', '${channel}_info.rb']))
+      .then((_) => runGit(['commit', '-a', '-m',
+                           'Updated $channel branch to revision $revision']))
+      .then((_) => runGit(['push']))
+      .whenComplete(() => new Directory(repository).delete(recursive: true));
+}