Rename updateStyle to updateRenderTree

updateStyle was doing too many things, this patch moves the style updating
logic out into a new function called updateStyle and renames the original
one to updateRenderTree. It also renames all the other updateStyle related
things to be named with "updateRenderTree".

Review URL: https://codereview.chromium.org/211773002

git-svn-id: svn://svn.chromium.org/blink/trunk@170012 bbb929c8-8fbe-4397-9dbb-9b2b20218538