[Tab Groups] Size group headers according to their title size.

Previously group headers were sized the same width as tabs, which would
give them lots of extra margin around the title chip when the tabs were
big and not enough margin when the tabs were small. This patch allows
tabstrip layout to use a different TabSizeInfo for each View, and gives
group headers a fixed width based on their title chip size.

Bug: 905491
Change-Id: I8705581633c1e6bf4a71fd4522a55391e8a4f54e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1721559
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Reviewed-by: Taylor Bergquist <tbergquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684126}
17 files changed