Revert "Adds a separator between custom tab bar and title, based on UX feedback."

This reverts commit f207ec9653d036442e5738a4740b04506d7fe346.

Reason for revert: suspected for https://bugs.chromium.org/p/chromium/issues/detail?id=923894#c14

Original change's description:
> Adds a separator between custom tab bar and title, based on UX feedback.
> 
> Previously, a similar separator was drawn. However, this separator
> was always shown (when the theme color was white-ish), and the desired
> behavior is to *only* render the separator when the custom tab bar
> is visible AND the custom tab bar is white-ish.
> 
> This CL will cause a 15% black separator to be drawn at the top of the
> custom tab bar, blended with the apps theme color, so it looks like
> the separator is drawn onto the title bar.
> 
> Bug: 918788
> Change-Id: Iba020fe4f059558fe355d18236d5226d35f3a2aa
> Reviewed-on: https://chromium-review.googlesource.com/c/1414535
> Commit-Queue: Jay Harris <harrisjay@chromium.org>
> Reviewed-by: Bret Sepulveda <bsep@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#624514}

TBR=bsep@chromium.org,harrisjay@chromium.org

Change-Id: I16e4607f127301e3c579277f92b2549b51a92266
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 918788, 923894
Reviewed-on: https://chromium-review.googlesource.com/c/1425999
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624638}
2 files changed