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

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

Index: pkg/front_end/lib/src/fasta/target_implementation.dart
diff --git a/pkg/front_end/lib/src/fasta/target_implementation.dart b/pkg/front_end/lib/src/fasta/target_implementation.dart
index d702e6e7473b41879e437a776ef016c0f0500046..142f1c70a7d147e4263ae3fb5bd0a15fbd42ce35 100644
--- a/pkg/front_end/lib/src/fasta/target_implementation.dart
+++ b/pkg/front_end/lib/src/fasta/target_implementation.dart
@@ -8,8 +8,14 @@ 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;
@@ -78,6 +84,11 @@ abstract class TargetImplementation extends Target {
     }
   }
 
+  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);
 }