Generate storage for -webkit-box-direction in ComputedStyleBase

Moved the inherited property -webkit-box-direction and its enum,
EBoxDirection, to be generated in ComputedStyleBase.

BUG=628043

Review-Url: https://codereview.chromium.org/2563353002
Cr-Commit-Position: refs/heads/master@{#438368}
4 files changed