Increase proactive suggestions chip max width.

Per discussion with UX, increasing max width from 240dp to 280dp and
making configurable in case feedback indicates we need to adjust this
value further.

Bug: b:140649426
Change-Id: I82d89ad96df5d0a9e4e1028fc8bd8fb291cd1f43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1793788
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696094}
3 files changed