add a bin/grind.dart and a bin/grinder.dart script

bin/grind.dart

@@ -0,0 +1,11 @@
+// Copyright 2014 Google. All rights reserved. Use of this source code is
+// governed by a BSD-style license that can be found in the LICENSE file.
+
+/**
+ * Look for `tool/grind.dart` relative to the current directory and run it.
+ */
+library grinder.grind;
+
+import 'grinder.dart' as g;
+
+void main(List args) => g.runScript('tool/grind.dart', args);

bin/grinder.dart

@@ -0,0 +1,39 @@
+// Copyright 2014 Google. All rights reserved. Use of this source code is
+// governed by a BSD-style license that can be found in the LICENSE file.
+
+/**
+ * Look for `tool/grinder.dart` relative to the current directory and run it.
+ */
+library grinder.grinder;
+
+import 'dart:io';
+
+void main(List args) => runScript('tool/grinder.dart', args);
+
+void runScript(String script, List args) {
+  File file = new File(script);
+
+  if (!file.existsSync()) {
+    print("Error: expected to find a '${script}' script.");
+    exit(1);
+  }
+
+  List newArgs = [script]..addAll(args);
+  _runProcessAsync(Platform.isWindows ? 'dart.exe' : 'dart', newArgs);
+}
+
+void _runProcessAsync(String executable, List<String> arguments) {
+  Process.start(executable, arguments).then((Process process) {
+    process.stdout.listen((List<int> data) {
+      stdout.write(new String.fromCharCodes(data));
+    });
+
+    process.stderr.listen((List<int> data) {
+      stderr.write(new String.fromCharCodes(data));
+    });
+
+    return process.exitCode.then((int code) {
+      if (code != 0) exit(code);
+    });
+  });
+}

lib/grinder.dart

@@ -115,7 +115,7 @@ ArgParser _createArgsParser() {
 }
 
 void _printUsage(ArgParser parser, Grinder grinder) {
-  print('usage: dart ${Platform.script} <options> target1 target2 ...');
+  print('usage: dart ${_currentScript()} <options> target1 target2 ...');
   print('');
   print('valid options:');
   print(parser.getUsage().replaceAll('\n\n', '\n'));
@@ -131,6 +131,15 @@ void _printUsage(ArgParser parser, Grinder grinder) {
   }
 }
 
+String _currentScript() {
+  String script = Platform.script.toString();
+  String uriBase = Uri.base.toString();
+  if (script.startsWith(uriBase)) {
+    script = script.substring(uriBase.length);
+  }
+  return script;
+}
+
 void _printDeps(Grinder grinder) {
   // calculate the dependencies
   grinder.start([], dontRun: true);