GitLab

The hovered tab state was visually too close to active state
so this CL reduces the opacity. The method for calculating
interpolation range and hover radial gradient opacity is
changed to use target contrast ratios. This approach ideally
will adapt better to various themes and color schemes,
ensuring the right level of contrast by adjusting opacity
automatically.

Bug: 856893
Change-Id: I2799b722c1d84d7c323e4f587fa8f5e58106bf58
Reviewed-on: https://chromium-review.googlesource.com/1147605
Commit-Queue: Orin Jaworski <orinj@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581330}