Add support for building patched_sdk and platform.dill for dart2js:

pkg/front_end/lib/src/fasta/source/directive_listener.dart

 // Copyright (c) 2017, 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.
 
 /// Listener used in combination with `TopLevelParser` to extract the URIs of
 /// import, part, and export directives.
 library front_end.src.fasta.source.directive_listener;
 
 import '../fasta_codes.dart' show FastaMessage, codeExpectedBlockToSkip;
-import '../parser/dart_vm_native.dart' show skipNativeClause;
 import '../parser/listener.dart';
 import '../quote.dart';
 import '../scanner/token.dart';
 
 /// Listener that records the URIs from imports, exports, and part directives.
 ///
 /// This is normally used in combination with the `TopLevelParser`, which skips
 /// over the body of declarations like classes and function that are irrelevant
 /// for directives. Note that on correct programs directives cannot occur after
 /// any top-level declaration, but we recommend to continue parsing the entire
 /// file in order to gracefully handle input errors.
 class DirectiveListener extends Listener {
-  /// Whether we accept the native-syntax used by the VM patch files.
-  final bool acceptsNativeClause;
-
   /// Collects URIs that occur on any import directive.
   final Set<String> imports = new Set<String>();
 
   /// Collects URIs that occur on any export directive.
   final Set<String> exports = new Set<String>();
 
   /// Collects URIs that occur on any part directive.
   final Set<String> parts = new Set<String>();
 
-  DirectiveListener({this.acceptsNativeClause: false});
+  DirectiveListener();
 
   /// Set when entering the context of a directive, null when the parser is not
   /// looking at a directive.
   Set<String> _current = null;
 
   bool get _inDirective => _current != null;
 
   @override
   beginImport(_) {
     _current = imports;
@@ skipping 26 matching lines @@
 
   @override
   void beginLiteralString(Token token) {
     if (_inDirective) {
       _current.add(unescapeString(token.lexeme));
     }
   }
 
   @override
   Token handleUnrecoverableError(Token token, FastaMessage message) {
-    if (acceptsNativeClause && message.code == codeExpectedBlockToSkip) {
-      Token recover = skipNativeClause(token);
+    if (message.code == codeExpectedBlockToSkip) {
+      Token recover = handleNativeClause(token);
       if (recover != null) return recover;
     }
     return super.handleUnrecoverableError(token, message);
   }
+
+  /// Defines how native clauses are handled. By default, they are not handled
+  /// and an error is thrown;
+  Token handleNativeClause(Token token) => null;
 }