Change RenderText::trimmedPrefWidths to specify text direction

Change the signature for RenderText::trimmedPrefWidths to require a
direction argument and update the RenderBlock callsite to specify the
desired direction.

BUG=333004
R=leviw@chromium.org

Review URL: https://codereview.chromium.org/148693002

git-svn-id: svn://svn.chromium.org/blink/trunk@165898 bbb929c8-8fbe-4397-9dbb-9b2b20218538