(DO NOT LAND) Revert of Generate StyleBackgroundData in ComputedStyleBase.

Revert of Generate StyleBackgroundData in ComputedStyleBase. (patchset #1 id:1 of https://codereview.chromium.org/2861623002/ )

Reason for revert:
Testing

Original issue's description:
> Generate StyleBackgroundData in ComputedStyleBase.
> 
> This patch generates the following fields as part of a group:
> - background ('storage_only' of type FillLayer)
> - background_color ('storage_only' of type Color)
> 
> Since both fields correspond to shorthands, we specify them in
> ComputedStyleExtraFields.json5.
> 
> All deleted code are correspondingly generated in
> ComputedStyleBase, apart from the line
> 
>   background_data_(o.background_data_)
> 
> which is implicit in the compiler generated ComputedStyleBase
> copy constructor.
> 
> Diff of generated files:
> https://gist.github.com/darrnshn/c2d2e7f7429b6281987c8f1ff6e2c313/revisions
> 
> BUG=628043
> 
> Review-Url: https://codereview.chromium.org/2861623002
> Cr-Commit-Position: refs/heads/master@{#469566}
> Committed: https://chromium.googlesource.com/chromium/src/+/8976caef37205d31c6b73aec7f008a652671f076

TBR=meade@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=628043

[shend, 2017-05-08 02:54:32]

Created Revert of Generate StyleBackgroundData in ComputedStyleBase.

[shend, 2017-05-08 03:04:28]

shend@chromium.org changed reviewers:
- meade@chromium.org