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Add it to (bubble) dialog's parent class so that it can be reused.
It is added to the top of the dialog.

Add some screenshots in bug comment 17 to visualize this change (It
will not be shown in the bubble in the screenshots, just to make it
easier to see what it will look like).

Bug: 991037
Change-Id: I4b18bfa510efbd585c50154c66613fc9a7c80b12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1830092
Commit-Queue: Siyu An <siyua@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703921}