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

pkg/front_end/tool/fasta_perf.dart

 // Copyright (c) 2017, 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.
 
 /// An entrypoint used to run portions of fasta and measure its performance.
 library front_end.tool.fasta_perf;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/src/fasta/ast_builder.dart';
 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;
 
 /// Cumulative time spent scanning.
 Stopwatch scanTimer = new Stopwatch();
 
 main(List<String> args) async {
   // TODO(sigmund): provide sdk folder as well.
   if (args.length < 2) {
@@ skipping 118 matching lines @@
       helper(uri.resolve(directiveUri));
     }
   }
 
   helper(start);
 }
 
 /// 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)
     ..addAll(listener.exports)
     ..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();
   var parseTimer = new Stopwatch()..start();
   files.forEach((uri, source) {
     parseFull(uri, source);
   });
   parseTimer.stop();
 
   report('scan', scanTimer.elapsedMicroseconds);
@@ skipping 67 matching lines @@
 /// Report that metric [name] took [time] micro-seconds to process
 /// [inputSize] characters.
 void report(String name, int time) {
   var sb = new StringBuffer();
   var padding = ' ' * (20 - name.length);
   sb.write('$name:$padding $time us, ${time ~/ 1000} ms');
   var invSpeed = (time * 1000 / inputSize).toStringAsFixed(2);
   sb.write(', $invSpeed ns/char');
   print('$sb');
 }