[Mac] Refactor BrowserWindowTouchBarMac

Separate BrowserWindowTouchBarMac into two classes:
BrowserWindowDefaultTouchBar and
BrowserWindowTouchBarController.

BrowserWindowTouchBarController determines what
touch bar should be used for browser window.
BrowserWindowDefaultTouchBar creates a default
touch bar for the browser.

These changes are split from a bigger change to
hook up touch bar support for web textfield in
MacViews:

https://chromium-review.googlesource.com/c/chromium/src/+/1132597

Bug: 856391
Change-Id: I9be31c65bd0acc2ec4d39b5e2f6b06fc30e36bf7
Reviewed-on: https://chromium-review.googlesource.com/1133705
Commit-Queue: Sarah Chan <spqchan@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574693}
13 files changed