Fix crash in ExtensionUninstallDialogViews::Show

Fixes regression in r728281. The code started assuming that a
BrowserActionsContainer always existed, this is not true for windows
without a tab strip.

Bug: chromium:1042419
Change-Id: Ia69257972ebe08d58a878722a42821730ebcc7b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003220
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@{#732258}

chrome/browser/ui/views/extensions/extension_uninstall_dialog_view.cc

@@ -135,10 +135,12 @@ void ExtensionUninstallDialogViews::Show() {
     anchor_view = container->GetViewForId(extension()->id());
   } else if (browser_view &&
              !base::FeatureList::IsEnabled(features::kExtensionsToolbarMenu)) {
+    BrowserActionsContainer* const browser_actions_container =
+        browser_view->toolbar_button_provider()->GetBrowserActionsContainer();
     ToolbarActionView* const reference_view =
-        browser_view->toolbar_button_provider()
-            ->GetBrowserActionsContainer()
-            ->GetViewForId(extension()->id());
+        browser_actions_container
+            ? browser_actions_container->GetViewForId(extension()->id())
+            : nullptr;
     if (reference_view && reference_view->GetVisible())
       anchor_view = reference_view;
   }