[LayoutNG] Add writing-mode and direction to NGFragmentBase

Add enum and fields for writing-mode and text-direction to the fragment
base class. Also change how the type is specified and adds a DCHECK for
setOffset ensuring it can only be called once.

BUG=635619
R=ikilpatrick@chromium.org, glebl@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2230803005
Cr-Commit-Position: refs/heads/master@{#411193}
5 files changed