Mash: Make Chrome update correct window's properties for immersive.

This makes ShelfLayoutManager::UpdateVisibilityState correctly update
state to SHELF_AUTO_HIDE, which triggers Shelf::AutoHideEventHandler,
which already works without updates.

Bug: 897968

Change-Id: Id2e5f785dbf24a0999088b13fe4971ee6758e32e
Reviewed-on: https://chromium-review.googlesource.com/c/1295176Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601809}

ash/shelf/shelf_layout_manager.h

@@ -108,7 +108,6 @@ class ASH_EXPORT ShelfLayoutManager
   // Invoked by the shelf when the auto-hide state may have changed.
   void UpdateAutoHideState();
 
-  // TODO(mash): Add similar event handling support for mash.
   // Updates the auto-hide state for mouse events.
   void UpdateAutoHideForMouseEvent(ui::MouseEvent* event, aura::Window* target);
 

chrome/browser/ui/views/frame/immersive_context_mus.cc

@@ -27,7 +27,8 @@ ImmersiveContextMus::~ImmersiveContextMus() {
 void ImmersiveContextMus::OnEnteringOrExitingImmersive(
     ash::ImmersiveFullscreenController* controller,
     bool entering) {
-  aura::Window* window = controller->widget()->GetNativeWindow();
+  aura::Window* window =
+      controller->widget()->GetNativeWindow()->GetRootWindow();
   // Auto hide the shelf in immersive fullscreen instead of hiding it.
   window->SetProperty(ash::kHideShelfWhenFullscreenKey, !entering);
   // Update the window's immersive mode state for the window manager.