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

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index fe5289180a6a853a853c82ff35c8e883cfc0c9fe..e001c5f2c5906e4ae2bfe340495b65eb63613e1f 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -1859,6 +1859,17 @@ void Isolate::PrintJSON(JSONStream* stream, bool ref) {
     JSONObject jssettings(&jsobj, "_debuggerSettings");
     debugger()->PrintSettingsToJSONObject(&jssettings);
   }
+
+  {
+    JSONArray extensions(&jsobj, "serviceExtensions");
+    GrowableObjectArray& handlers =
+        GrowableObjectArray::Handle(registered_service_extension_handlers());
+    String& handler_name = String::Handle();
+    for (intptr_t i = 0; i < handlers.Length(); i += kRegisteredEntrySize) {
+      handler_name ^= handlers.At(i + kRegisteredNameIndex);
+      extensions.AddValue(handler_name.ToCString());
+    }
+  }
 }
 
 
@@ -2042,6 +2053,12 @@ void Isolate::RegisterServiceExtensionHandler(const String& name,
   handlers.Add(name, Heap::kOld);
   ASSERT(kRegisteredHandlerIndex == 1);
   handlers.Add(closure, Heap::kOld);
+  {
+    // Fire off an event.
+    ServiceEvent event(this, ServiceEvent::kIsolateServiceExtensionRegistered);
+    event.set_extension_name(&name);
+    Service::HandleEvent(&event);
+  }
 }