Revert of Separate CSSValueID mappings generator from ComputedStyleBase generator. (patchset #3 id:40001 of https://codereview.chromium.org/2794853002/ )

Reason for revert:
Broke compilation on Google Chrome Mac bot

BUG=710778

Original issue's description:
> Separate CSSValueID mappings generator from ComputedStyleBase generator.
>
> We currently generate mappings between CSSValueID and platform enums
> inside the ComputedStyleBase generator. However, because such mappings
> do not exist for nonproperty fields, it no longer makes sense for us
> to generate these mappings inside make_computed_style_base.py.
>
> This patch moves the generator for CSSValueIDMappingsGenerated to
> its own file, so that it is not affected by nonproperty fields.
>
> BUG=628043
>
> Review-Url: https://codereview.chromium.org/2794853002
> Cr-Commit-Position: refs/heads/master@{#463955}
> Committed: https://chromium.googlesource.com/chromium/src/+/dea75f9603af994dd10370ddd25a0dc6af7b93cd

TBR=bugsnash@chromium.org,meade@chromium.org,shend@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=628043

Review-Url: https://codereview.chromium.org/2812823004
Cr-Commit-Position: refs/heads/master@{#463966}
3 files changed