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

pkg/front_end/lib/src/fasta/source/outline_builder.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.outline_builder;
 
 import 'package:kernel/ast.dart' show AsyncMarker, ProcedureKind;
 
 import '../fasta_codes.dart' show FastaMessage, codeExpectedBlockToSkip;
 
@@ skipping 10 matching lines @@
 import '../errors.dart' show internalError;
 
 import '../builder/builder.dart';
 
 import '../modifier.dart' show Modifier;
 
 import 'source_library_builder.dart' show SourceLibraryBuilder;
 
 import 'unhandled_listener.dart' show NullValue, Unhandled, UnhandledListener;
 
+import '../parser/dart2js_native.dart' show skipDart2jsNativeClause;
+
 import '../parser/dart_vm_native.dart'
-    show removeNativeClause, skipNativeClause;
+    show removeNativeClause, skipVmNativeClause;
 
 import '../operator.dart'
     show
         Operator,
         operatorFromString,
         operatorToString,
         operatorRequiredArgumentCount;
 
 import '../quote.dart' show unescapeString;
 
@@ skipping 758 matching lines @@
 
   @override
   void handleModifiers(int count) {
     debugEvent("Modifiers");
     push(popList(count) ?? NullValue.Modifiers);
   }
 
   @override
   Token handleUnrecoverableError(Token token, FastaMessage message) {
     if (isDartLibrary && message.code == codeExpectedBlockToSkip) {
-      Token recover = skipNativeClause(token);
-      if (recover != null) {
-        nativeMethodName = unescapeString(token.next.lexeme);
-        return recover;
+      if (library.loader.target.forDart2js) {
+        Token recover = skipDart2jsNativeClause(token);
+        if (recover != null) return recover;
+      } else if (library.loader.target.forVm) {
+        Token recover = skipVmNativeClause(token);
+        if (recover != null) {
+          nativeMethodName = unescapeString(token.next.lexeme);
+          return recover;
+        }
       }
     }
     return super.handleUnrecoverableError(token, message);
   }
 
   @override
   Link<Token> handleMemberName(Link<Token> identifiers) {
     if (!isDartLibrary || identifiers.isEmpty) return identifiers;
     return removeNativeClause(identifiers);
   }
 
   @override
   void debugEvent(String name) {
     // printEvent(name);
   }
 }