Run clang-modernize -use-nullptr over src/extensions/.

extensions/browser/app_window/app_window.cc

Index: extensions/browser/app_window/app_window.cc
diff --git a/extensions/browser/app_window/app_window.cc b/extensions/browser/app_window/app_window.cc
index 6481dc7cb00580efdb6fafbdbcc65760eaac9e5e..54e376ac46c9b82a6b0193661c76d2ebff720742 100644
--- a/extensions/browser/app_window/app_window.cc
+++ b/extensions/browser/app_window/app_window.cc
@@ -442,7 +442,7 @@ void AppWindow::OnNativeClose() {
   if (app_window_contents_) {
     WebContents* web_contents = app_window_contents_->GetWebContents();
     WebContentsModalDialogManager::FromWebContents(web_contents)
-        ->SetDelegate(NULL);
+        ->SetDelegate(nullptr);
     app_window_contents_->NativeWindowClosed();
   }
   delete this;