[M63 Merge][Locked Fullscreen] Fix URL click tablet mode bug followup

Follow-up to crrev.com/c/1439080 - use GetRootWindow() if we're using window
service.

TBR=pkotwicz@chromium.org

(cherry picked from commit 6115145ea3747781cfda2463e988dc078d8f70d5)

Bug: 888684
Change-Id: Ifb531e9e12984048eb124c487f52ce8753cda08d
Reviewed-on: https://chromium-review.googlesource.com/c/1445894
Reviewed-by: Ivan Šandrk <isandrk@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Ivan Šandrk <isandrk@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#627479}
Reviewed-on: https://chromium-review.googlesource.com/c/1447712
Cr-Commit-Position: refs/branch-heads/3683@{#88}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
diff --git a/chrome/browser/ui/views/frame/immersive_mode_controller_ash.cc b/chrome/browser/ui/views/frame/immersive_mode_controller_ash.cc
index afc0730..8f3dfc5 100644
--- a/chrome/browser/ui/views/frame/immersive_mode_controller_ash.cc
+++ b/chrome/browser/ui/views/frame/immersive_mode_controller_ash.cc
@@ -198,7 +198,9 @@
 
   // Don't use immersive mode as long as we are in the locked fullscreen mode
   // since immersive shows browser controls which allow exiting the mode.
-  if (ash::IsWindowTrustedPinned(widget->GetNativeWindow()))
+  aura::Window* window = widget->GetNativeWindow();
+  window = features::IsUsingWindowService() ? window->GetRootWindow() : window;
+  if (ash::IsWindowTrustedPinned(window))
     return;
 
   // Enable immersive mode if the widget is activated. Do not disable immersive