Create DomAgent and CSSAgent in Chrome.

chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc

Index: chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
diff --git a/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc b/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
index b5486da2d5674d4a2886b4c6d77b7eeb0f4ec5f8..04e64603d731ff8a5944f62d56347d6bdb515e84 100644
--- a/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
+++ b/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
@@ -15,6 +15,9 @@
 
 #if defined(USE_AURA)
 #include "base/run_loop.h"
+#include "components/ui_devtools/devtools_server.h"
+#include "components/ui_devtools/views/ui_devtools_css_agent.h"
+#include "components/ui_devtools/views/ui_devtools_dom_agent.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/service_manager_connection.h"
 #include "services/service_manager/public/cpp/connector.h"
@@ -102,6 +105,19 @@ void ChromeBrowserMainExtraPartsViews::PreProfileInit() {
   // IME driver must be available at login screen, so initialize before profile.
   if (service_manager::ServiceManagerIsRemote())
     IMEDriver::Register();
+
+  // Start devtools server
+  devtools_server_ = ui_devtools::UiDevToolsServer::Create(nullptr);
+  if (devtools_server_) {
+    auto dom_backend = base::MakeUnique<ui_devtools::UIDevToolsDOMAgent>();
+    auto css_backend =
+        base::MakeUnique<ui_devtools::UIDevToolsCSSAgent>(dom_backend.get());
+    auto devtools_client = base::MakeUnique<ui_devtools::UiDevToolsClient>(
+        "UiDevToolsClient", devtools_server_.get());
+    devtools_client->AddAgent(std::move(dom_backend));
+    devtools_client->AddAgent(std::move(css_backend));
+    devtools_server_->AttachClient(std::move(devtools_client));
+  }
 #endif
 
 #if defined(OS_LINUX) && !defined(OS_CHROMEOS)