Provide list of service protocol extensions in isolate and emit an event when one is registered

runtime/observatory/tests/service/developer_extension_test.dart

Index: runtime/observatory/tests/service/developer_extension_test.dart
diff --git a/runtime/observatory/tests/service/developer_extension_test.dart b/runtime/observatory/tests/service/developer_extension_test.dart
index f134606fb66b6bdf0b2ab4dac38d6b785cd4ba9d..daa8685606c890215f7c9ed9093e017a127a3c59 100644
--- a/runtime/observatory/tests/service/developer_extension_test.dart
+++ b/runtime/observatory/tests/service/developer_extension_test.dart
@@ -55,6 +55,7 @@ Future<ServiceExtensionResponse> LanguageErrorHandler(String method,
 
 void test() {
   registerExtension('__delay', Handler);
+  debugger();
   registerExtension('__error', Handler);
   registerExtension('__exception', Handler);
   registerExtension('__null', Handler);
@@ -71,6 +72,17 @@ void test() {
 }
 
 var tests = [
+  hasStoppedAtBreakpoint,
+  (Isolate isolate) async {
+    await isolate.load();
+    expect(isolate.serviceExtensions.length, 1);
+    expect(isolate.serviceExtensions[0], equals('__delay'));
+  },
+  resumeIsolateAndAwaitEvent(VM.kIsolateStream, (ServiceEvent event) {
+    // Check that we received an event when '__error' was registered.
+    expect(event.kind, equals(ServiceEvent.kServiceExtensionAdded));
+    expect(event.serviceExtensionName, equals('__error'));
+  }),
   // Initial.
   (Isolate isolate) async {
     var result;
@@ -130,4 +142,4 @@ var tests = [
   },
 ];
 
-main(args) async => runIsolateTests(args, tests, testeeBefore:test);
+main(args) async => runIsolateTests(args, tests, testeeConcurrent:test);