Do not JSON encode the 'result' of a service rpc.

runtime/vm/json_stream.cc

Index: runtime/vm/json_stream.cc
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 06c13fc645efc95043c7a72242c861576ee33a26..f894c712fedc1b5794c33d4624a46cd9df89dd76 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -22,6 +22,7 @@ JSONStream::JSONStream(intptr_t buf_size)
     : open_objects_(0),
       buffer_(buf_size),
       reply_port_(ILLEGAL_PORT),
+      seq_(""),
       method_(""),
       param_keys_(NULL),
       param_values_(NULL),
@@ -35,10 +36,12 @@ JSONStream::~JSONStream() {
 
 void JSONStream::Setup(Zone* zone,
                        Dart_Port reply_port,
+                       const String& seq,
                        const String& method,
                        const Array& param_keys,
                        const Array& param_values) {
   set_reply_port(reply_port);
+  seq_ = seq.ToCString();
   method_ = method.ToCString();
 
   String& string_iterator = String::Handle();
@@ -66,6 +69,13 @@ void JSONStream::Setup(Zone* zone,
               isolate_name, method_);
     setup_time_micros_ = OS::GetCurrentTimeMicros();
   }
+  buffer_.Printf("{\"result\":");
+}
+
+
+void JSONStream::SetupError() {
+  buffer_.Clear();
+  buffer_.Printf("{\"error\":");
 }
 
 
@@ -83,6 +93,8 @@ void JSONStream::PostReply() {
   if (FLAG_trace_service) {
     process_delta_micros = OS::GetCurrentTimeMicros() - setup_time_micros_;
   }
+  // TODO(turnidge): Handle non-string sequence numbers.
+  buffer_.Printf(", \"id\":\"%s\"}", seq());
   const String& reply = String::Handle(String::New(ToCString()));
   ASSERT(!reply.IsNull());