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

pkg/kernel/lib/target/targets.dart

Index: pkg/kernel/lib/target/targets.dart
diff --git a/pkg/kernel/lib/target/targets.dart b/pkg/kernel/lib/target/targets.dart
index 7389dc073975ac9726a1db5356a3e626a9a70199..5618162b9a9070b2cc77b48c959e20cbe0f44798 100644
--- a/pkg/kernel/lib/target/targets.dart
+++ b/pkg/kernel/lib/target/targets.dart
@@ -114,6 +114,29 @@ abstract class Target {
   void performGlobalTransformations(CoreTypes coreTypes, Program program,
       {void logger(String msg)});
 
+  /// Whether a platform library may define a restricted type, such as `bool`,
+  /// `int`, `double`, `num`, and `String`.
+  ///
+  /// By default only `dart:core` may define restricted types, but some target
+  /// implementations override this.
+  bool mayDefineRestrictedType(Uri uri) =>
+      uri.scheme == 'dart' && uri.path == 'core';
+
+  /// Whether the `native` language extension is supported within [library].
+  ///
+  /// The `native` language extension is not part of the language specification,
+  /// it means something else to each target, and it is enabled under different
+  /// circumstances 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.
+  bool enableNative(Uri uri) => false;
+
+  /// There are two variants of the `native` language extension. The VM expects
+  /// the native token to be followed by string, whereas dart2js and DDC do not.
+  // TODO(sigmund, ahe): ideally we should remove the `native` syntax, if not,
+  // we should at least unify the VM and non-VM variants.
+  bool get nativeExtensionExpectsString => false;
+
   /// Builds an expression that instantiates an [Invocation] that can be passed
   /// to [noSuchMethod].
   Expression instantiateInvocation(CoreTypes coreTypes, Expression receiver,