Fix default theme color on dark mode on tab restore

https://chromium-review.googlesource.com/c/chromium/src/+/1501952
accidentally removed the logic for not saving default theme color
in TabState so that it doesn't get restored persistently in either
light or dark mode. Bringing back the check for whether default theme
color is used.

Bug: 942605
Change-Id: Ieddae24331369e9bceb95992bb891255ace4a413
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1524985
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641258}
1 file changed