R1:7b1b146620b5

Save, then restore scroll position in Chrome textareas on remarkup assist

Summary:
Fixes T10396. Seems like this has been around for a while (references from 2011):

http://stackoverflow.com/questions/4002312/chrome-resets-the-textarea-scroll-bar-scrolltop-when-focus-is-called
https://bugs.chromium.org/p/chromium/issues/detail?id=75072

Commenting out this `focus()` seemed to fix the issue locally, at the cost of not focusing.

Saving, focusing, then restoring seems to produce the correct behavior…