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

pkg/front_end/tool/fasta_perf.dart

Index: pkg/front_end/tool/fasta_perf.dart
diff --git a/pkg/front_end/tool/fasta_perf.dart b/pkg/front_end/tool/fasta_perf.dart
index 5a2d6e04e00ab2c2f9d113373964c9f1ed50c1ad..1b1d4c75ab89e2f255c9db0ffaaf90e76e1ae71f 100644
--- a/pkg/front_end/tool/fasta_perf.dart
+++ b/pkg/front_end/tool/fasta_perf.dart
@@ -13,12 +13,14 @@ import 'package:front_end/src/fasta/dill/dill_target.dart' show DillTarget;
 import 'package:front_end/src/fasta/kernel/kernel_target.dart'
     show KernelTarget;
 import 'package:front_end/src/fasta/parser.dart';
-import 'package:front_end/src/fasta/source/directive_listener.dart';
 import 'package:front_end/src/fasta/scanner.dart';
 import 'package:front_end/src/fasta/scanner/io.dart' show readBytesFromFileSync;
+import 'package:front_end/src/fasta/source/directive_listener.dart';
 import 'package:front_end/src/fasta/ticker.dart' show Ticker;
 import 'package:front_end/src/fasta/translate_uri.dart' show TranslateUri;
 import 'package:front_end/src/fasta/translate_uri.dart';
+import 'package:front_end/src/fasta/parser/dart_vm_native.dart'
+    show skipNativeClause;
 
 /// Cumulative total number of chars scanned.
 int inputSize = 0;
@@ -157,7 +159,7 @@ Future<Null> collectSources(Uri start, Map<Uri, List<int>> files) async {
 /// Parse [contents] as a Dart program and return the URIs that appear in its
 /// import, export, and part directives.
 Set<String> extractDirectiveUris(List<int> contents) {
-  var listener = new DirectiveListener(acceptsNativeClause: true);
+  var listener = new DirectiveListenerWithNative();
   new TopLevelParser(listener).parseUnit(tokenize(contents));
   return new Set<String>()
     ..addAll(listener.imports)
@@ -165,6 +167,11 @@ Set<String> extractDirectiveUris(List<int> contents) {
     ..addAll(listener.parts);
 }
 
+class DirectiveListenerWithNative extends DirectiveListener {
+  @override
+  Token handleNativeClause(Token token) => skipNativeClause(token);
+}
+
 /// Parses every file in [files] and reports the time spent doing so.
 void parseFiles(Map<Uri, List<int>> files) {
   scanTimer = new Stopwatch();