[PM] Hook the tab helper to WebUILoginView's WebView

The PerformanceManagerTabHelper reflects WebContents and their frame
trees into the PerformanceManager graph. This CL gives the graph
visibility for the ChromeOS login's view.

Bug: 993029
Change-Id: Ie1822ba72f64df9d29084e7bf2c42526273f86e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2017928
Auto-Submit: Patrick Monette <pmonette@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735663}

chrome/browser/chromeos/BUILD.gn

@@ -206,6 +206,7 @@ source_set("chromeos") {
     "//components/ownership",
     "//components/password_manager/core/browser",
     "//components/password_manager/core/browser:hash_password_manager",
+    "//components/performance_manager",
     "//components/permissions",
     "//components/policy:generated",
     "//components/policy/core/browser",

chrome/browser/chromeos/login/ui/webui_login_view.cc

@@ -38,6 +38,7 @@
 #include "chromeos/network/network_state_handler.h"
 #include "components/content_settings/core/common/content_settings_pattern.h"
 #include "components/password_manager/core/browser/password_manager.h"
+#include "components/performance_manager/embedder/performance_manager_registry.h"
 #include "components/session_manager/core/session_manager.h"
 #include "components/web_modal/web_contents_modal_dialog_manager.h"
 #include "content/public/browser/notification_service.h"
@@ -219,6 +220,9 @@ void WebUILoginView::InitializeWebView(views::WebView* web_view,
       web_contents->GetMutableRendererPrefs();
   renderer_preferences_util::UpdateFromSystemSettings(
       prefs, ProfileHelper::GetSigninProfile());
+
+  performance_manager::PerformanceManagerRegistry::GetInstance()
+      ->CreatePageNodeForWebContents(web_contents);
 }
 
 void WebUILoginView::Init() {