First cut at _spawnUri rpc in the vm service.

runtime/vm/service_event.cc

Index: runtime/vm/service_event.cc
diff --git a/runtime/vm/service_event.cc b/runtime/vm/service_event.cc
index 94af480e8fc45697967b94685ea18487e82ede05..3ff1e1b001694192442314fd828c586d2e1fb15e 100644
--- a/runtime/vm/service_event.cc
+++ b/runtime/vm/service_event.cc
@@ -23,6 +23,8 @@ ServiceEvent::ServiceEvent(Isolate* isolate, EventKind event_kind)
       extension_rpc_(NULL),
       exception_(NULL),
       reload_error_(NULL),
+      spawn_token_(NULL),
+      spawn_error_(NULL),
       at_async_jump_(false),
       inspectee_(NULL),
       gc_stats_(NULL),
@@ -69,6 +71,8 @@ const char* ServiceEvent::KindAsCString() const {
       return "ServiceExtensionAdded";
     case kIsolateReload:
       return "IsolateReload";
+    case kIsolateSpawn:
+      return "IsolateSpawn";
     case kPauseStart:
       return "PauseStart";
     case kPauseExit:
@@ -122,6 +126,7 @@ const StreamInfo* ServiceEvent::stream_info() const {
     case kIsolateExit:
     case kIsolateUpdate:
     case kIsolateReload:
+    case kIsolateSpawn:
     case kServiceExtensionAdded:
       return &Service::isolate_stream;
 
@@ -183,6 +188,16 @@ void ServiceEvent::PrintJSON(JSONStream* js) const {
       jsobj.AddProperty("reloadError", *(reload_error()));
     }
   }
+  if (kind() == kIsolateSpawn) {
+    ASSERT(spawn_token() != NULL);
+    jsobj.AddPropertyStr("spawnToken", *(spawn_token()));
+    if (spawn_error_ == NULL) {
+      jsobj.AddProperty("status", "success");
+    } else {
+      jsobj.AddProperty("status", "failure");
+      jsobj.AddPropertyStr("spawnError", *(spawn_error()));
+    }
+  }
   if (kind() == kServiceExtensionAdded) {
     ASSERT(extension_rpc_ != NULL);
     jsobj.AddProperty("extensionRPC", extension_rpc_->ToCString());