SplitSettings: Close OS settings drawer menu when exiting narrow mode

Port this behavior from browser settings to OS settings:
https://chromium-review.googlesource.com/c/chromium/src/+/1611137

The tests are not ported yet because we're still setting up our test
scaffolding for the OS settings pages: crbug.com/955731

Bug: 950007
Change-Id: I5e64081fa1d573d3984c3b8d63e61df46bc481ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1628676
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663356}
1 file changed