Pass a TaskRunner through ViewsDelegate to put AX init on FILE thread

ui/views/views_delegate.cc

Index: ui/views/views_delegate.cc
diff --git a/ui/views/views_delegate.cc b/ui/views/views_delegate.cc
index 4c1ae4f6b90ae5d70eba822e96959723e7ae3a04..770ff542040a7264eeeef342a4c3f17259f48be2 100644
--- a/ui/views/views_delegate.cc
+++ b/ui/views/views_delegate.cc
@@ -91,6 +91,10 @@ std::string ViewsDelegate::GetApplicationName() {
   return program.BaseName().AsUTF8Unsafe();
 }
 
+scoped_refptr<base::TaskRunner> ViewsDelegate::GetInitializationTaskRunner() {
+  return nullptr;
+}
+
 #if defined(OS_WIN)
 int ViewsDelegate::GetAppbarAutohideEdges(HMONITOR monitor,
                                           const base::Closure& callback) {