Fix for select PopupMenuList appearance in rtl mode with overlay-scrollbar enabled.

The content should take total window width while overlay-scrollbar is enabled. 

BUG=382900

Review URL: https://codereview.chromium.org/333633003

git-svn-id: svn://svn.chromium.org/blink/trunk@176261 bbb929c8-8fbe-4397-9dbb-9b2b20218538