Turn dart2js into a shell script.

dart/lib/compiler/implementation/dart2js.dart

 // Copyright (c) 2012, 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('dart2js');
 
 #import('dart:io');
 #import('dart:uri');
 #import('dart:utf');
 
 #import('../compiler.dart', prefix: 'api');
 #import('colors.dart');
 #import('source_file.dart');
 #import('filenames.dart');
 #import('util/uri_extras.dart');
 
+final String LIBRARY_ROOT = '../../../..';
+
 void compile(List<String> argv) {
   Uri cwd = getCurrentDirectory();
   bool throwOnError = false;
   bool showWarnings = true;
   bool verbose = false;
   Uri libraryRoot = cwd;
   Uri out = cwd.resolve('out.js');
   List<String> options = new List<String>();
 
   List<String> arguments = <String>[];
@@ skipping 100 matching lines @@
   var buffer = new List<int>(length);
   var bytes = file.readListSync(buffer, 0, length);
   file.closeSync();
   return new String.fromCharCodes(new Utf8Decoder(buffer).decodeRest());
 }
 
 void fail(String message) {
   print(message);
   exit(1);
 }
+
+void compilerMain(Options options) {
+  List<String> argv = ['--library-root=${options.script}/$LIBRARY_ROOT'];
+  argv.addAll(options.arguments);
+  compile(argv);
+}
+
+void main() {
+  try {
+    compilerMain(new Options());
+  } catch (var exception, var trace) {
+    try {
+      print('Internal error: \$exception');
+    } catch (var ignored) {
+      print('Internal error: error while printing exception');
+    }
+    try {
+      print(trace);
+    } finally {
+      exit(253); // 253 is recognized as a crash by our test scripts.
+    }
+  }
+}