Port _echo, etc commands to RPC

runtime/vm/service/service.idl

 //
 // TODO(turnidge): Finish writing an idl description of the service protocol.
 //
 
 interface Service {
   // Returns the list of breakpoints for an isolate.
   getBreakpoints(isolateId string) BreakpointList
 
   // Adds a breakpoint at the specified line.
   //
@@ skipping 63 matching lines @@
                        targetId string,
                        limit int) InboundReferences
 
   getClassList(isolateId string) ClassList
 
   // When <code>onlyWithInstantiations</code> is true, the list only includes
   // type arguments with instantiations. Otherwise, all type arguments are
   // 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
 }
 
 
 // Every top level response returned by the Service interface extends
 // <code>Response</code>.  This allows the client to distinguish
 // between different kinds of responses by using the <code>type</code>
 // property.
 struct Response {
   // Every response returned by the VM Service has the
   // <code>type</code> property.  This allows the client distinguish
   // between different kinds of responses.
   type    string
 
   // Some responses will have the <code>_vmType</code> property.  This
   // provides the VM-internal type name of an object, and is provided
   // only when this type name differs from the <code>type</code>
   // property.
   _vmType string [optional]
 }
 
 
+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
   // object inside the vm or an isolate.
   id  string
 }
 
 
 // An <code>Instance</code> represents a Dart-language object.
 struct Instance extends Object {
@@ skipping 214 matching lines @@
 // A <code>TagSelector</code> is used to indicate which sets of tags
 // should take precedence in a cpu profile.
 enum TagSelector {
   UserVM
   UserOnly
   VMUser
   VMOnly
   None
 }