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

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

Index: pkg/front_end/lib/src/fasta/target_implementation.dart
diff --git a/pkg/front_end/lib/src/fasta/target_implementation.dart b/pkg/front_end/lib/src/fasta/target_implementation.dart
index 58781f6c1f174de970228bfff5e244d876dff0c6..4bf7ed8dfea85b29e4ce14cf8eb17d80f70687f2 100644
--- a/pkg/front_end/lib/src/fasta/target_implementation.dart
+++ b/pkg/front_end/lib/src/fasta/target_implementation.dart
@@ -8,14 +8,8 @@ import 'package:kernel/target/targets.dart' as backend show Target;
 
 import 'builder/builder.dart' show Builder, ClassBuilder, LibraryBuilder;
 
-import 'parser/dart_vm_native.dart' as vm show skipNativeClause;
-
-import '../scanner/token.dart' show Token;
-
 import 'loader.dart' show Loader;
 
-import 'quote.dart' show unescapeString;
-
 import 'target.dart' show Target;
 
 import 'ticker.dart' show Ticker;
@@ -102,25 +96,6 @@ abstract class TargetImplementation extends Target {
     }
   }
 
-  /// Whether the `native` language extension is supported within [library].
-  ///
-  /// The `native` language extension is not part of the language specification,
-  /// means something else to each target, and is enabled differently for each
-  /// target implementation. For example, the VM target enables it everywhere
-  /// because of existing support for "dart-ext:" native extensions, but targets
-  /// like dart2js only enable it on the core libraries.
-  ///
-  /// This default implementation assumes a VM target, but it can be overriden
-  /// in subclasses to change the behavior.
-  // TODO(sigmund,ahe): limit this to `dart-ext` libraries only (see
-  // https://github.com/dart-lang/sdk/issues/29763).
-  bool enableNative(LibraryBuilder library) => true;
-
-  Token skipNativeClause(Token token) => vm.skipNativeClause(token);
-
-  String extractNativeMethodName(Token token) =>
-      unescapeString(token.next.lexeme);
-
   void addSourceInformation(
       Uri uri, List<int> lineStarts, List<int> sourceCode);