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

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

Index: pkg/front_end/lib/src/fasta/fasta.dart
diff --git a/pkg/front_end/lib/src/fasta/fasta.dart b/pkg/front_end/lib/src/fasta/fasta.dart
index ccc2196bba61bc756994dd4b1a9e20b4eed8a1de..d044beb24e773ca3bacb74230415071775be7133 100644
--- a/pkg/front_end/lib/src/fasta/fasta.dart
+++ b/pkg/front_end/lib/src/fasta/fasta.dart
@@ -111,15 +111,16 @@ class CompileTask {
 
   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) {
@@ -174,10 +175,11 @@ Future<CompilationResult> parseScript(
     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);
@@ -209,13 +211,16 @@ Future<CompilationResult> parseScript(
 }
 
 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);
   });
 }
@@ -224,7 +229,8 @@ 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 {
@@ -232,14 +238,17 @@ Future writeDepsFile(Uri script, Uri depsFile, Uri output,
     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);