Remove public methods on StyleBoxData and rename member.

This patch does two things:
- Remove public methods on StyleBoxData. This is because these methods
  will no longer exist once we generate StyleBoxData.
- Rename vertical_align_ -> vertical_align_length_, to differentiate it
  from the keyword part of vertical-align (also called vertical_align_,
  stored in ComputedStyleBase)

This is preparation for generating StyleBoxData.

BUG=628043

Review-Url: https://codereview.chromium.org/2844163002
Cr-Commit-Position: refs/heads/master@{#467606}
4 files changed