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

pkg/front_end/lib/src/fasta/source/diet_listener.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.diet_listener;
 
 import 'package:front_end/src/fasta/kernel/kernel_ast_factory.dart'
     show KernelAstFactory;
 
 import 'package:front_end/src/fasta/type_inference/type_inference_engine.dart'
     show TypeInferenceEngine;
 
 import 'package:kernel/ast.dart' show AsyncMarker;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
 
 import 'package:kernel/core_types.dart' show CoreTypes;
 
 import '../fasta_codes.dart' show FastaMessage, codeExpectedBlockToSkip;
 
 import '../parser/parser.dart' show Parser, optional;
 
 import '../scanner/token.dart' show BeginGroupToken, Token;
 
-import '../parser/dart_vm_native.dart'
-    show removeNativeClause, skipNativeClause;
+import '../parser/dart_vm_native.dart' show removeNativeClause;
 
 import '../util/link.dart' show Link;
 
 import '../errors.dart' show Crash, InputError, inputError, internalError;
 
 import 'stack_listener.dart' show StackListener;
 
 import '../kernel/body_builder.dart' show BodyBuilder;
 
 import '../builder/builder.dart';
@@ skipping 439 matching lines @@
   void endNamedMixinApplication(Token beginToken, Token classKeyword,
       Token equals, Token implementsKeyword, Token endToken) {
     debugEvent("NamedMixinApplication");
     pop(); // Name.
     checkEmpty(beginToken.charOffset);
   }
 
   @override
   Token handleUnrecoverableError(Token token, FastaMessage message) {
     if (isDartLibrary && message.code == codeExpectedBlockToSkip) {
-      Token recover = skipNativeClause(token);
-      if (recover != null) {
-        assert(isTargetingDartVm);
-        return recover;
-      }
+      Token recover = library.loader.target.skipNativeClause(token);
+      if (recover != null) return recover;
     }
     return super.handleUnrecoverableError(token, message);
   }
 
   @override
   Link<Token> handleMemberName(Link<Token> identifiers) {
     if (!isDartLibrary || identifiers.isEmpty) return identifiers;
     return removeNativeClause(identifiers);
   }
 
@@ skipping 61 matching lines @@
     }
     if (builder == null) {
       return internalError("Builder not found: $name", uri, token.charOffset);
     }
     if (builder.next != null) {
       return inputError(uri, token.charOffset, "Duplicated name: $name");
     }
     return builder;
   }
 
-  bool get isTargetingDartVm {
-    // TODO(ahe): Find a more reliable way to check if this is the Dart VM.
-    return !coreTypes.containsLibrary("dart:_js_helper");
-  }
-
   @override
   void debugEvent(String name) {
     // printEvent(name);
   }
 }