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This reverts commit 8c35e22c.

Reason for revert: Reverting to fix unit_tests on chromeos bot. This is next in the chain. Ugh!

Original change's description:
> Add background tab colors and inactive images to the theme system.
> 
> These will eventually be used for three purposes:
> (1) To allow generating different background tab images from a common tint for
>     the inactive and incognito cases, thus allowing background tabs that blend
>     into the frame for custom themes.
> (2) To allow autogenerating the background tab colors from the background tab
>     images, thus letting us autocalculate better tab text/separator/etc. colors.
> (3) To allow theme authors to customize/override this behavior more precisely.
> 
> Reasons (1) and (2) dictated the design here; reason (3) is basically a free
> bonus.  I thought about not making these resources overrideable by theme
> authors, but there was some technical reason that turned out to not be easily
> feasible, and there seems little reason to prevent it.
> 
> This also allows us to read THEME_TAB_BACKGROUND_INCOGNITO on Mac (Views).
> 
> This shouldn't result in a visual change on its own.
> 
> Bug: 862664
> Change-Id: Icc57f78fd526d68b83c692fbac669a7371bb38ff
> Reviewed-on: https://chromium-review.googlesource.com/1147869
> Commit-Queue: Peter Kasting <pkasting@chromium.org>
> Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
> Reviewed-by: Evan Stade <estade@chromium.org>
> Reviewed-by: Allen Bauer <kylixrd@chromium.org>
> Reviewed-by: Bret Sepulveda <bsep@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#578790}

TBR=pkasting@chromium.org,oshima@chromium.org,estade@chromium.org,bsep@chromium.org,kylixrd@chromium.org

Change-Id: I6abe212768916890c11aec28aac5fc96891ac695
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 862664
Reviewed-on: https://chromium-review.googlesource.com/1153990Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578861}