Remove Cocoa Dependency from BrowserWindowTouchBar

To make the BrowserWindowTouchBar available to MacViews,
modify the class so that it no longer depends on Cocoa
code to receive updates for the touch bar item states.

This CL converts BookmarkTabHelperDelegate to
BookmarkTabHelperObserver so that BrowserWindowTouchBar
can observe the current web contents for starred changes.

Overview CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1086867

Bug: 841714
Change-Id: Id8944ad085d87288bcda767a53bb1abfe5c0eab9
Reviewed-on: https://chromium-review.googlesource.com/1090315
Commit-Queue: Sarah Chan <[email protected]>
Reviewed-by: Elly Fong-Jones <[email protected]>
Cr-Commit-Position: refs/heads/master@{#565570}
17 files changed