HTMLFormControlElement::didRecalcStyle doesn't need to use PostAttachCallbacks

Near as I can tell updateFromElement() can no longer cause the selection to
change so lets stop using PostAttachCallbacks. This leaves only
scheduleLayerUpdate and autofocus using post attach callbacks. A future patch
will move autofocus off it and then we can make PostAttachCallbacks specific
to the layer updating system (and hopefully remove that usage someday too).

Review URL: https://codereview.chromium.org/131153002

git-svn-id: svn://svn.chromium.org/blink/trunk@165048 bbb929c8-8fbe-4397-9dbb-9b2b20218538