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

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

Index: pkg/front_end/lib/src/fasta/source/diet_listener.dart
diff --git a/pkg/front_end/lib/src/fasta/source/diet_listener.dart b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
index 750a3d838cf13b243400c8b381329a63b0dad209..f0f69848121e59ee479b7a8476e0c09e0f230449 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -22,8 +22,10 @@ import '../parser/parser.dart' show Parser, optional;
 
 import '../scanner/token.dart' show BeginGroupToken, Token;
 
+import '../parser/dart2js_native.dart' show skipDart2jsNativeClause;
+
 import '../parser/dart_vm_native.dart'
-    show removeNativeClause, skipNativeClause;
+    show removeNativeClause, skipVmNativeClause;
 
 import '../util/link.dart' show Link;
 
@@ -482,11 +484,13 @@ class DietListener extends StackListener {
   @override
   Token handleUnrecoverableError(Token token, FastaMessage message) {
     if (isDartLibrary && message.code == codeExpectedBlockToSkip) {
-      Token recover = skipNativeClause(token);
-      if (recover != null) {
-        assert(isTargetingDartVm);
-        return recover;
+      Token recover;
+      if (library.loader.target.forDart2js) {

[ahe, 2017/04/27 13:34:34]

Could be in a subclass?

[Siggi Cherem (dart-lang), 2017/04/28 21:37:20]

Moved this into the target instead.

+        recover = skipDart2jsNativeClause(token);
+      } else if (library.loader.target.forVm) {
+        recover = skipVmNativeClause(token);
       }
+      if (recover != null) return recover;
     }
     return super.handleUnrecoverableError(token, message);
   }
@@ -568,11 +572,6 @@ class DietListener extends StackListener {
     return builder;
   }
 
-  bool get isTargetingDartVm {
-    // TODO(ahe): Find a more reliable way to check if this is the Dart VM.
-    return !coreTypes.containsLibrary("dart:_js_helper");
-  }
-
   @override
   void debugEvent(String name) {
     // printEvent(name);