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

pkg/front_end/lib/src/fasta/target_implementation.dart

 // Copyright (c) 2016, 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 fasta.target_implementation;
 
 import 'package:kernel/target/vm.dart' show VmTarget;
 
 import 'builder/builder.dart' show Builder, ClassBuilder, LibraryBuilder;
 
+import 'parser/dart_vm_native.dart' as vm show skipNativeClause;
+
+import 'scanner/token.dart' show Token;
+
 import 'loader.dart' show Loader;
 
+import 'quote.dart' show unescapeString;
+
 import 'target.dart' show Target;
 
 import 'ticker.dart' show Ticker;
 
 import 'translate_uri.dart' show TranslateUri;
 
 /// Provides the implementation details used by a loader for a target.
 abstract class TargetImplementation extends Target {
   final TranslateUri uriTranslator;
   Builder cachedCompileTimeError;
@@ skipping 48 matching lines @@
     LibraryBuilder internal = loader.read(Uri.parse("dart:_internal"));
     return cachedNativeAnnotation = internal.getConstructor("ExternalName");
   }
 
   void loadExtraRequiredLibraries(Loader loader) {
     for (String uri in new VmTarget(null).extraRequiredLibraries) {
       loader.read(Uri.parse(uri));
     }
   }
 
+  Token skipNativeClause(Token token) => vm.skipNativeClause(token);
+
+  String extractNativeMethodName(Token token) =>
+      unescapeString(token.next.lexeme);
+
   void addSourceInformation(
       Uri uri, List<int> lineStarts, List<int> sourceCode);
 }