Fix update_homebrew script for releasing Dart on Mac using homebrew.

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
index f85968a58f1054b6e72844496519e7387a58e0ae..1fe8f0ad4026e6a724d9dff53e945190ead2140d 100644
--- a/tools/apps/update_homebrew/bin/update_homebrew.dart
+++ b/tools/apps/update_homebrew/bin/update_homebrew.dart
@@ -50,7 +50,7 @@ Future writeHomebrewInfo(String channel, int revision) {
       final file = "channels/$channel/release/$revision/${files[key]}";
       buffer.writeln('  ${key}_FILE = "$file"');
       buffer.writeln('  ${key}_HASH = "$hash"');
-    })
+    });
   })
     .then((_) => getVersion(channel, revision))
     .then((version) {
@@ -80,6 +80,11 @@ main(args) {
   final options = parser.parse(args);
   final revision = options['revision'];
   final channel = options['channel'];
+  if ([revision, channel, options['key']].contains(null)) {
+    print("Usage: update_homebrew.dart -r revision -c channel -k ssh_key\n"
+          "  ssh_key should allow pushes to dart-lang/homebrew-dart on github");
+    return;
+  }
   final sshWrapper = Platform.script.resolve('ssh_with_key').toFilePath();
   gitEnvironment = {'GIT_SSH': sshWrapper,
                     'SSH_KEY_PATH': options['key']};
@@ -91,7 +96,6 @@ main(args) {
       .then((_) => runGit(
           ['clone', 'git@github.com:dart-lang/homebrew-dart.git', '.']))
       .then((_) => writeHomebrewInfo(channel, revision))
-      .then((_) => runGit(['add', '${channel}_info.rb']))

[Bill Hesse, 2014/10/01 14:18:43]

Now that the files are in the repository, the -a option to git commit adds
changes to them to the commit.

       .then((_) => runGit(['commit', '-a', '-m',
                            'Updated $channel branch to revision $revision']))
       .then((_) => runGit(['push']))