Allow Dart code to register service protocol handlers

runtime/vm/service.h

Index: runtime/vm/service.h
diff --git a/runtime/vm/service.h b/runtime/vm/service.h
index 3b23f6d553bd7c0902311de5a7f3bc4d0733ec1e..662a8f32efdb86eeccbe1a2c812220bc5203f94b 100644
--- a/runtime/vm/service.h
+++ b/runtime/vm/service.h
@@ -144,7 +144,12 @@ class Service : public AllStatic {
 
   static EmbedderServiceHandler* FindIsolateEmbedderHandler(const char* name);
   static EmbedderServiceHandler* FindRootEmbedderHandler(const char* name);
-
+  static bool ExtensionHandlerExists(const String& name);
+  static bool InvokeExtensionHandler(const String& name,
+                                     const Array& parameter_keys,
+                                     const Array& parameter_values,
+                                     const Array& response);
+  static void PostExtensionResponse(const Array& response, JSONStream* js);
   static void SendEvent(const char* stream_id,
                         const char* event_type,
                         const Object& eventMessage);