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 93 matching lines @@
 }
 
 class CompileTask {
   final CompilerContext c;
   final Ticker ticker;
 
   CompileTask(this.c, this.ticker);
 
   KernelTarget createKernelTarget(
       DillTarget dillTarget, TranslateUri uriTranslator, bool strongMode) {
-    return new KernelTarget(
-        dillTarget, uriTranslator, strongMode, c.uriToSource);
+    return new KernelTarget(dillTarget, uriTranslator, strongMode,
+        c.options.targetDart2js, 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 =
+        new DillTarget(ticker, uriTranslator, c.options.targetDart2js);
     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 34 matching lines @@
       return new CompilationResult.error(
           formatUnexpected(patchedSdk, -1, "Patched sdk directory not found."));
     }
 
     Target target = getTarget("vm", new TargetFlags(strongMode: false));
 
     Program program;
     try {
       TranslateUri uriTranslator = await TranslateUri.parse(null, packages);
       final Ticker ticker = new Ticker(isVerbose: verbose);
-      final DillTarget dillTarget = new DillTarget(ticker, uriTranslator);
+      final DillTarget dillTarget =
+          new DillTarget(ticker, uriTranslator, false);
       dillTarget.read(patchedSdk.resolve('platform.dill'));
       final KernelTarget kernelTarget =
-          new KernelTarget(dillTarget, uriTranslator, strongMode);
+          new KernelTarget(dillTarget, uriTranslator, strongMode, false);
       kernelTarget.read(fileName);
       await dillTarget.writeOutline(null);
       program = await kernelTarget.writeOutline(null);
       program = await kernelTarget.writeProgram(null);
       if (kernelTarget.errors.isNotEmpty) {
         return new CompilationResult.errors(kernelTarget.errors
             .map((err) => err.toString())
             .toList(growable: false));
       }
     } on InputError catch (e) {
@@ skipping 11 matching lines @@
     // Write the program to a list of bytes and return it.
     var sink = new ByteSink();
     new BinaryPrinter(sink).writeProgramFile(program);
     return new CompilationResult.ok(sink.builder.takeBytes());
   } catch (e, s) {
     return reportCrash(e, s, fileName);
   }
 }
 
 Future compilePlatform(Uri patchedSdk, Uri output,
-    {Uri packages, bool verbose: false}) async {
+    {Uri packages, bool verbose: false, bool targetDart2js: false}) async {
   Ticker ticker = new Ticker(isVerbose: verbose);
   await CompilerCommandLine.withGlobalOptions("", [""], (CompilerContext c) {
     c.options.options["--packages"] = packages;
     if (verbose) {
       c.options.options["--verbose"] = true;
     }
+    if (targetDart2js) {
+      c.options.options["--target"] = "dart2js";
+    }
     return compilePlatformInternal(c, ticker, patchedSdk, output);
   });
 }
 
 Future writeDepsFile(Uri script, Uri depsFile, Uri output,
     {Uri packages,
     Uri platform,
     Iterable<Uri> extraDependencies,
-    bool verbose: false}) async {
+    bool verbose: false,
+    bool targetDart2js: false}) async {
   Ticker ticker = new Ticker(isVerbose: verbose);
   await CompilerCommandLine.withGlobalOptions("", [""],
       (CompilerContext c) async {
     c.options.options["--packages"] = packages;
     if (verbose) {
       c.options.options["--verbose"] = true;
     }
+    if (targetDart2js) {
+      c.options.options["--target"] = "dart2js";
+    }
 
     TranslateUri uriTranslator =
         await TranslateUri.parse(c.options.sdk, c.options.packages);
     ticker.logMs("Read packages file");
-    DillTarget dillTarget = new DillTarget(ticker, uriTranslator)
+    DillTarget dillTarget = new DillTarget(ticker, uriTranslator, targetDart2js)
       ..read(platform);
-    KernelTarget kernelTarget =
-        new KernelTarget(dillTarget, uriTranslator, false, c.uriToSource);
+    KernelTarget kernelTarget = new KernelTarget(
+        dillTarget, uriTranslator, false, targetDart2js, c.uriToSource);
 
     kernelTarget.read(script);
     await dillTarget.writeOutline(null);
     await kernelTarget.loader.buildOutlines();
     await kernelTarget.writeDepsFile(output, depsFile,
         extraDependencies: extraDependencies);
   });
 }
 
 // TODO(ahe): https://github.com/dart-lang/sdk/issues/28316
 class ByteSink implements Sink<List<int>> {
   final BytesBuilder builder = new BytesBuilder();
 
   void add(List<int> data) {
     builder.add(data);
   }
 
   void close() {
     // Nothing to do.
   }
 }