Turn dart2js into a shell script.

dart/lib/compiler/implementation/dart2js.dart

Index: dart/lib/compiler/implementation/dart2js.dart
diff --git a/dart/lib/compiler/implementation/dart2js.dart b/dart/lib/compiler/implementation/dart2js.dart
index 347b1bfdc15d5a65dcbb90a055ec09cd71ba0d70..63e477fb79abd620a4da8427c3d1c066b870ad56 100644
--- a/dart/lib/compiler/implementation/dart2js.dart
+++ b/dart/lib/compiler/implementation/dart2js.dart
@@ -14,6 +14,8 @@
 #import('filenames.dart');
 #import('util/uri_extras.dart');
 
+final String LIBRARY_ROOT = '../../../..';
+
 void compile(List<String> argv) {
   Uri cwd = getCurrentDirectory();
   bool throwOnError = false;
@@ -134,3 +136,26 @@ 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.
+    }
+  }
+}