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

pkg/kernel/lib/target/vm.dart

Index: pkg/kernel/lib/target/vm.dart
diff --git a/pkg/kernel/lib/target/vm.dart b/pkg/kernel/lib/target/vm.dart
index 2733d35a8d166a672e24aee9e85120a3422aa2f3..a108928d2f576cc56db31552fa045496b7d885df 100644
--- a/pkg/kernel/lib/target/vm.dart
+++ b/pkg/kernel/lib/target/vm.dart
@@ -269,4 +269,12 @@ class VmTarget extends Target {
           new NamedExpression("growable", new BoolLiteral(false))
         ]));
   }
+
+  // TODO(sigmund,ahe): limit this to `dart-ext` libraries only (see
+  // https://github.com/dart-lang/sdk/issues/29763).
+  @override
+  bool enableNative(Uri uri) => true;
+
+  @override
+  bool get nativeExtensionExpectsString => true;
 }