[Extensions Menu] Adjust CHECKs in BrowserView

Adjust the CHECKs in BrowserView to avoid triggering a CHECK failure
when there is no extensions container (which can happen in the case
of app windows). This fixes
AppBrowserControllerBrowserTest.NoExtensionsContainerExists with the
menu enabled.

Bug: 943702
Change-Id: Id14113c456934f5e7984d142f97104929080da32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153745Reviewed-by: Caroline Rising <corising@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760187}

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

@@ -1367,14 +1367,13 @@ void BrowserView::FocusToolbar() {
 }
 
 ExtensionsContainer* BrowserView::GetExtensionsContainer() {
-  ExtensionsToolbarContainer* const extensions_toolbar_container =
-      toolbar_button_provider_->GetExtensionsToolbarContainer();
-  if (extensions_toolbar_container)
-    return extensions_toolbar_container;
+  if (base::FeatureList::IsEnabled(features::kExtensionsToolbarMenu))
+    return toolbar_button_provider_->GetExtensionsToolbarContainer();
 
-  CHECK(!base::FeatureList::IsEnabled(features::kExtensionsToolbarMenu));
   BrowserActionsContainer* container =
       toolbar_button_provider_->GetBrowserActionsContainer();
+  // Note that in some cases (such as an app window), there is no extensions
+  // container.
   return container ? container->toolbar_actions_bar() : nullptr;
 }