The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c35f4bc4f6115ad02485318c5bd3c560c7533698

commit c35f4bc4f6115ad02485318c5bd3c560c7533698
Author: Matthew Jones <mdjones@chromium.org>
Date: Tue May 15 19:56:02 2018

Fix more issues with scrim and bottom sheet

This patch removes a check that causes the scrim to remain visable
after the bottom sheet is closed. The check in question blocked offset
change events if the bottom sheet is closed, but in certain cases like
when the sheet doesn't animate, the sheets state is closed before any
offset events occur.

This patch also adds a BottomSheetObserver when the sheet is opened
that controls the opacity of the scrim and removes it when the sheet
is closed.

Bug:  842902 ,842765
Change-Id: Ic70532cefa0ddcafc06d0a2b3a5b6e28639ff24e
Reviewed-on: https://chromium-review.googlesource.com/1058437
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558814}
[modify] https://crrev.com/c35f4bc4f6115ad02485318c5bd3c560c7533698/chrome/android/java/src/org/chromium/chrome/browser/widget/bottomsheet/BottomSheetController.java