TabGridDialog UI Polish

* Shift the grid in dialog up by 8dp.
* Put dialog title in the correct position and modify the text
appearance.
* Replace the original hide dialog button with back arrow.
* Round the corners of the dialog by 8dp.

Bug: 977273
Change-Id: Id0df26d12264dca313ad4554f8e115366e1d5bc8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674924
Commit-Queue: Yue Zhang <yuezhanggg@google.com>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672222}
5 files changed