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

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

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index 34fd49fe5cac6f483360547f31bb67e1092e835b..7fada005de1a4bab3e0a32c74812e471aef5d8ad 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -34,7 +34,9 @@ import 'package:kernel/core_types.dart' show CoreTypes;
 
 import 'frontend_accessors.dart' show buildIsNull, makeBinary, makeLet;
 
-import '../parser/dart_vm_native.dart' show skipNativeClause;
+import '../parser/dart2js_native.dart' show skipDart2jsNativeClause;
+
+import '../parser/dart_vm_native.dart' show skipVmNativeClause;
 
 import '../scanner/token.dart'
     show BeginGroupToken, Token, isBinaryOperator, isMinusOperator;
@@ -2493,8 +2495,13 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
   @override
   Token handleUnrecoverableError(Token token, FastaMessage message) {
     if (isDartLibrary && message.code == codeExpectedFunctionBody) {
-      Token recover = skipNativeClause(token);
-      if (recover != null) return recover;
+      if (library.loader.target.forDart2js) {

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

Can we move this to a subclass of BodyBuilder?

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

this moved to the target, which is easier to override once in package:compiler.
I still would like to get rid of the extra logic for this, so I added some TODOs
about it.

+        Token recover = skipDart2jsNativeClause(token);
+        if (recover != null) return recover;
+      } else {
+        Token recover = skipVmNativeClause(token);
+        if (recover != null) return recover;
+      }
     } else if (message.code == codeExpectedButGot) {
       String expected = message.arguments["string"];
       const List<String> trailing = const <String>[")", "}", ";", ","];