Add support for compiling Dart via the FE in dart2js.

pkg/compiler/lib/src/apiimpl.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 leg_apiimpl;
 
 import 'dart:async';
 
 import 'package:package_config/packages.dart';
 import 'package:package_config/packages_file.dart' as pkgs;
@@ skipping 121 matching lines @@
   }
 
   Future<Script> _synthesizeScript(Uri readableUri) {
     return new Future.value(new Script.synthetic(readableUri));
   }
 
   Future<Binary> readBinary(Uri resourceUri, [Spannable node]) {
     if (!resourceUri.isAbsolute) {
       if (node == null) node = NO_LOCATION_SPANNABLE;
       reporter.internalError(
-          node, 'Relative uri $resourceUri provided to readScript(Uri).');
+          node, 'Relative uri $resourceUri provided to readBinary(Uri).');
     }
 
     // We need to store the current element since we are reporting read errors
     // asynchronously and therefore need to restore the current element for
     // [node] to be valid.
     elements.Element element = currentElement;
 
     return new Future.sync(
             () => callUserProvider(resourceUri, api.InputKind.binary))
         .catchError((error) {
@@ skipping 265 matching lines @@
   }
 }
 
 /// For every 'dart:' library, a corresponding environment variable is set
 /// to "true". The environment variable's name is the concatenation of
 /// this prefix and the name (without the 'dart:'.
 ///
 /// For example 'dart:html' has the environment variable 'dart.library.html' set
 /// to "true".
 const String _dartLibraryEnvironmentPrefix = 'dart.library.';