Allow root level requests in the vm service.

runtime/vm/json_stream.h

Index: runtime/vm/json_stream.h
===================================================================
--- runtime/vm/json_stream.h	(revision 31848)
+++ runtime/vm/json_stream.h	(working copy)
@@ -5,6 +5,7 @@
 #ifndef VM_JSON_STREAM_H_
 #define VM_JSON_STREAM_H_
 
+#include "include/dart_api.h"  // for Dart_Port
 #include "platform/json.h"
 #include "vm/allocation.h"
 
@@ -25,10 +26,13 @@
   TextBuffer* buffer() { return &buffer_; }
   const char* ToCString() { return buffer_.buf(); }
 
+  void set_reply_port(Dart_Port port);
   void SetArguments(const char** arguments, intptr_t num_arguments);
   void SetOptions(const char** option_keys, const char** option_values,
                   intptr_t num_options);
 
+  Dart_Port reply_port() const { return reply_port_; }
+
   intptr_t num_arguments() const { return num_arguments_; }
   const char* GetArgument(intptr_t i) const {
     return arguments_[i];
@@ -77,6 +81,7 @@
 
   intptr_t open_objects_;
   TextBuffer buffer_;
+  Dart_Port reply_port_;
   const char** arguments_;
   intptr_t num_arguments_;
   const char** option_keys_;