Tweak public APIs and use them in patch_sdk, dart2js, and kernel-service

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 0a2be2bd99acc854a6c2d7f9b3d4f4e0928229ca..3f7557d1bff3436940651af7a6545f8666548eba 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -17,6 +17,8 @@ import '../parser/parser.dart'
 
 import '../parser/identifier_context.dart' show IdentifierContext;
 
+import '../parser/native_support.dart' show skipNativeClause;
+
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart';
 
 import 'package:front_end/src/fasta/kernel/utils.dart' show offsetForToken;
@@ -93,6 +95,7 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
   final Scope enclosingScope;
 
   final bool enableNative;
+  final bool stringExpectedAfterNative;
 
   /// Whether to ignore an unresolved reference to `main` within the body of
   /// `_getMainClosure` when compiling the current library.
@@ -180,7 +183,10 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
       this._typeInferrer)
       : enclosingScope = scope,
         library = library,
-        enableNative = library.loader.target.enableNative(library),
+        enableNative =
+            library.loader.target.backendTarget.enableNative(library.uri),
+        stringExpectedAfterNative =
+            library.loader.target.backendTarget.nativeExtensionExpectsString,
         ignoreMainInGetMainClosure = library.uri.scheme == 'dart' &&
             (library.uri.path == "_builtin" || library.uri.path == "ui"),
         needsImplicitSuperInitializer =
@@ -2974,7 +2980,7 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
   @override
   Token handleUnrecoverableError(Token token, FastaMessage message) {
     if (enableNative && message.code == codeExpectedFunctionBody) {
-      Token recover = library.loader.target.skipNativeClause(token);
+      Token recover = skipNativeClause(token, stringExpectedAfterNative);
       if (recover != null) return recover;
     } else if (message.code == codeExpectedButGot) {
       String expected = message.arguments["string"];