Update ash to use new devtools base agent

ash/common/wm_shell.cc

Index: ash/common/wm_shell.cc
diff --git a/ash/common/wm_shell.cc b/ash/common/wm_shell.cc
index da3bb1d99889a48445bfe23ebbe7ec003e9ff701..0c398ffd660d45b3a12e84511e82aabcf7cde294 100644
--- a/ash/common/wm_shell.cc
+++ b/ash/common/wm_shell.cc
@@ -93,7 +93,7 @@ void WmShell::Initialize(const scoped_refptr<base::SequencedWorkerPool>& pool) {
     auto dom_backend = base::MakeUnique<devtools::AshDevToolsDOMAgent>(this);
     auto devtools_client = base::MakeUnique<ui::devtools::UiDevToolsClient>(
         "Ash", devtools_server_.get());
-    devtools_client->AddDOMBackend(std::move(dom_backend));
+    devtools_client->AddAgent(std::move(dom_backend));
     devtools_server_->AttachClient(std::move(devtools_client));
   }
 }