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

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

Index: pkg/front_end/lib/src/fasta/source/outline_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/source/outline_builder.dart b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
index 12ef5d5bea8ff34e7e9b2cc88bcc67d35f83f5da..179cb32aee953f2cb9d840efb6f3003932f9a078 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -28,8 +28,10 @@ import 'source_library_builder.dart' show SourceLibraryBuilder;
 
 import 'unhandled_listener.dart' show NullValue, Unhandled, UnhandledListener;
 
+import '../parser/dart2js_native.dart' show skipDart2jsNativeClause;
+
 import '../parser/dart_vm_native.dart'
-    show removeNativeClause, skipNativeClause;
+    show removeNativeClause, skipVmNativeClause;
 
 import '../operator.dart'
     show
@@ -808,10 +810,15 @@ class OutlineBuilder extends UnhandledListener {
   @override
   Token handleUnrecoverableError(Token token, FastaMessage message) {
     if (isDartLibrary && message.code == codeExpectedBlockToSkip) {
-      Token recover = skipNativeClause(token);
-      if (recover != null) {
-        nativeMethodName = unescapeString(token.next.lexeme);
-        return recover;
+      if (library.loader.target.forDart2js) {
+        Token recover = skipDart2jsNativeClause(token);
+        if (recover != null) return recover;
+      } else if (library.loader.target.forVm) {
+        Token recover = skipVmNativeClause(token);
+        if (recover != null) {
+          nativeMethodName = unescapeString(token.next.lexeme);
+          return recover;
+        }
       }
     }
     return super.handleUnrecoverableError(token, message);