Add FeatureList CHECK to ::GetToolbarActionsBar()

This doesn't exist when kExtensionsToolbarMenu is on, so add a CHECK to
make sure it isn't used or gives reasonable stack traces if it does hit.

Bug: chromium:984654, chromium:985834
Change-Id: Ia1fde8b28dc39414cc378bda425a3d2775f0b359
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715245
Commit-Queue: Peter Boström <pbos@chromium.org>
Commit-Queue: Caroline Rising <corising@chromium.org>
Auto-Submit: Peter Boström <pbos@chromium.org>
Reviewed-by: Caroline Rising <corising@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680082}

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

@@ -66,6 +66,7 @@
 #include "chrome/browser/ui/tabs/tab_menu_model.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/browser/ui/tabs/tab_utils.h"
+#include "chrome/browser/ui/ui_features.h"
 #include "chrome/browser/ui/view_ids.h"
 #include "chrome/browser/ui/views/accelerator_table.h"
 #include "chrome/browser/ui/views/accessibility/invert_bubble_view.h"
@@ -1163,6 +1164,8 @@ void BrowserView::FocusToolbar() {
 }
 
 ToolbarActionsBar* BrowserView::GetToolbarActionsBar() {
+  CHECK(!base::FeatureList::IsEnabled(features::kExtensionsToolbarMenu));
+
   BrowserActionsContainer* container =
       toolbar_button_provider_->GetBrowserActionsContainer();
   return container ? container->toolbar_actions_bar() : nullptr;