The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6dd0dd3398afff807cc3d1940e1211779cba52e6

commit 6dd0dd3398afff807cc3d1940e1211779cba52e6
Author: spqchan <spqchan@chromium.org>
Date: Sat Nov 11 00:44:07 2017

[Mac] Make Touch Bar Observe the Command Updater

Currently the touch bar back/forward items get
updated when the page reloads or the active tab
has changed.

However, this can cause an issue in the future
where the back/forward items is not updated. This
CL fixes this but making BrowserWindowTouchbar
observe the back and forward commands.

The back/forward items will be updated according to
the commands changes instead of the page loads.


A unit test is added in BrowserWindowTouchBarUnitTest
for this change. In addition,
BrowserWindowTouchBarTest.PageLoadInvalidate is updated
so that we have better test coverage.

Bug:  783294 
Change-Id: Ic554543eb26088a5f4419decd8cc22f970ee2861
Reviewed-on: https://chromium-review.googlesource.com/761710
Commit-Queue: Sarah Chan <spqchan@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515767}
[modify] https://crrev.com/6dd0dd3398afff807cc3d1940e1211779cba52e6/chrome/browser/ui/cocoa/browser_window_touch_bar.h
[modify] https://crrev.com/6dd0dd3398afff807cc3d1940e1211779cba52e6/chrome/browser/ui/cocoa/browser_window_touch_bar.mm
[modify] https://crrev.com/6dd0dd3398afff807cc3d1940e1211779cba52e6/chrome/browser/ui/cocoa/browser_window_touch_bar_browsertest.mm
[modify] https://crrev.com/6dd0dd3398afff807cc3d1940e1211779cba52e6/chrome/browser/ui/cocoa/browser_window_touch_bar_unittest.mm