Fix nullptr crash in ExtensionUninstallDialogView

GetExtensionAnchorView() previously assumed that
GetBrowserActionsContainer() would always return a non-nullptr. This is
not the case for browser instances that do not support
Browser::FEATURE_TABSTRIP as most elements of ToolbarView are not
initialized (including |browser_actions_|).

Bug: chromium:892119
Change-Id: If67939cbe3c0174106848ce7339b789114391599
Reviewed-on: https://chromium-review.googlesource.com/c/1269176Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597634}

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

@@ -43,9 +43,13 @@ ToolbarActionView* GetExtensionAnchorView(const std::string& extension_id,
       BrowserView::GetBrowserViewForNativeWindow(window);
   if (!browser_view)
     return nullptr;
-  ToolbarActionView* reference_view = browser_view->toolbar_button_provider()
-                                          ->GetBrowserActionsContainer()
-                                          ->GetViewForId(extension_id);
+  DCHECK(browser_view->toolbar_button_provider());
+  BrowserActionsContainer* const browser_actions_container =
+      browser_view->toolbar_button_provider()->GetBrowserActionsContainer();
+  if (!browser_actions_container)
+    return nullptr;
+  ToolbarActionView* const reference_view =
+      browser_actions_container->GetViewForId(extension_id);
   return reference_view && reference_view->visible() ? reference_view : nullptr;
 }