[DevTools] migrate InspectorDOMAgent to new style

ash/common/devtools/ash_devtools_dom_agent.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/devtools/ash_devtools_dom_agent.h"
 
 #include "ash/common/wm_window.h"
 #include "components/ui_devtools/devtools_server.h"
 #include "ui/views/view.h"
 #include "ui/views/widget/widget.h"
@@ skipping 80 matching lines @@
 
 std::unique_ptr<ui::devtools::protocol::DOM::Node>
 AshDevToolsDOMAgent::BuildInitialTree() {
   std::unique_ptr<Array<DOM::Node>> children = Array<DOM::Node>::create();
   for (ash::WmWindow* window : shell_->GetAllRootWindows()) {
     children->addItem(BuildTreeForWindow(window));
   }
   return BuildNode("root", nullptr, std::move(children));
 }
 
-void AshDevToolsDOMAgent::getDocument(
-    ui::devtools::protocol::ErrorString* error,
+ui::devtools::protocol::Response AshDevToolsDOMAgent::enable() {
+  return ui::devtools::protocol::Response::OK();
+}
+
+ui::devtools::protocol::Response AshDevToolsDOMAgent::disable() {
+  return ui::devtools::protocol::Response::OK();
+}
+
+ui::devtools::protocol::Response AshDevToolsDOMAgent::getDocument(
     std::unique_ptr<ui::devtools::protocol::DOM::Node>* out_root) {
   *out_root = BuildInitialTree();
+  return ui::devtools::protocol::Response::OK();
 }
 
 }  // namespace devtools
 }  // namespace ash