Allow root level requests in the vm service.

runtime/vm/service.h

Index: runtime/vm/service.h
===================================================================
--- runtime/vm/service.h	(revision 31674)
+++ runtime/vm/service.h	(working copy)
@@ -13,10 +13,15 @@
 
 class Instance;
 class Isolate;
+class RawInstance;
 
 class Service : public AllStatic {
  public:
-  static void HandleServiceMessage(Isolate* isolate, const Instance& message);
+  // Handles a message which is not directed to an isolate.
+  static void HandleRootMessage(const Instance& message);
+
+  // Handles a message which is directed to a particular isolate.
+  static void HandleIsolateMessage(Isolate* isolate, const Instance& message);
 };
 
 }  // namespace dart