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

pkg/front_end/lib/src/fasta/fasta.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;
 
 import 'dart:async' show Future;
 
 import 'dart:convert' show JSON;
 
@@ skipping 92 matching lines @@
     return null;
   }
 }
 
 class CompileTask {
   final CompilerContext c;
   final Ticker ticker;
 
   CompileTask(this.c, this.ticker);
 
+  DillTarget createDillTarget(TranslateUri uriTranslator) {
+    return new DillTarget(ticker, uriTranslator);
+  }
+
   KernelTarget createKernelTarget(
       DillTarget dillTarget, TranslateUri uriTranslator, bool strongMode) {
     return new KernelTarget(
         dillTarget, uriTranslator, strongMode, c.uriToSource);
   }
 
   Future<KernelTarget> buildOutline([Uri output]) async {
     TranslateUri uriTranslator =
         await TranslateUri.parse(c.options.sdk, c.options.packages);
     ticker.logMs("Read packages file");
-    DillTarget dillTarget = new DillTarget(ticker, uriTranslator);
+    DillTarget dillTarget = createDillTarget(uriTranslator);
     KernelTarget kernelTarget =
         createKernelTarget(dillTarget, uriTranslator, c.options.strongMode);
     if (c.options.strongMode) {
       print("Note: strong mode support is preliminary and may not work.");
     }
     Uri platform = c.options.platform;
     if (platform != null) {
       dillTarget.read(platform);
     }
     String argument = c.options.arguments.first;
@@ skipping 129 matching lines @@
   final BytesBuilder builder = new BytesBuilder();
 
   void add(List<int> data) {
     builder.add(data);
   }
 
   void close() {
     // Nothing to do.
   }
 }