Port _echo, etc commands to RPC

runtime/vm/service/service.idl

Index: runtime/vm/service/service.idl
diff --git a/runtime/vm/service/service.idl b/runtime/vm/service/service.idl
index 80d43c590dd02f6583b354157132b292a7d40ef7..f10ccc796165dce21156b0bdb2edc969c6afb783 100644
--- a/runtime/vm/service/service.idl
+++ b/runtime/vm/service/service.idl
@@ -81,6 +81,21 @@ interface Service {
   // returned.
   getTypeArgumentsList(isolateId string,
                        onlyWithInstantiations bool) TypeArgumentsList
+
+  _echo(isolateId string,
+        text string) _EchoResponse
+
+  _echoVM(text string) _EchoResponse
+
+  // Triggers a ServiceEvent with EventType '_Echo'.
+  _triggerEchoEvent(isolateId string,
+                    text string) _EchoResponse
+
+  // Response is bad JSON.
+  _respondWithMalformedJson(isolateId string) Response
+
+  // Response is not an object.
+  _respondWithMalformedObject(isolateId string) Response
 }
 
 
@@ -102,6 +117,11 @@ struct Response {
 }
 
 
+struct _EchoResponse extends Response {
+  text string
+}
+
+
 // Persistent objects in the vm are returned as subclasses of Object.
 struct Object extends Response {
   // The object <code>id</code> can be used to refer to a persistent