Generate StyleBoxData in ComputedStyleBase.

This patch generates the following fields as part of a group:
- width and height ('storage_only' of type Length)
- min-width and min-height ('storage_only' of type Length)
- max-width and max-height ('storage_only' of type Length)
- VerticalAlignLength ('storage_only' of type Length)
- z-index ('storage_only' of type int)
- HasAutoZIndex ('storage_only' of type bool)
- box-sizing ('storage_only' of type EBoxSizing)
- box-decoration-break ('storage_only' of type EBoxSizing)

A few CSS properties are specified in ComputedStyleExtraFields.json5
rather than CSSProperties.json5:
- VerticalAlignLength, since we can't generate unions yet.
- box-sizing, will specify in CSSProperties.json5 in a separate patch
- box-decoration-break, will specify in CSSProperties.json5 in a
  separate patch

Future patches will also:
- Change (/min/max)(width/height) to be external fields so their
  getters/setters can be generated.
- Change box-sizing to be a keyword field so their getters/setters can
  be generated.
- Change box-decoration-break to be a keyword field so their
  getters/setters can be generated.

Diff of generated files:
https://gist.github.com/85b78bfcaf9ec0d78ea33eea24a49d9f/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2844183002
Cr-Commit-Position: refs/heads/master@{#471202}
4 files changed