[Mac] Don't Display Text Suggestions Touch Bar without Suggestions

If there are no suggestions, the touch bar will show an empty
NSCandidateListTouchBarItem. Instead of showing that, the browser
window touch bar should appear if there are no suggestions.

TextSuggestionsTouchBarControllerTest.MakeTouchBar was modified to
test that a text suggestions touch bar is not created if there are
no suggestions.

Bug: 717553
Change-Id: I2eb3286e5a96b97bb8d7737ddf6db352698804b8
Reviewed-on: https://chromium-review.googlesource.com/1173407
Reviewed-by: Sarah Chan <spqchan@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Tessa Nijssen <tnijssen@google.com>
Cr-Commit-Position: refs/heads/master@{#582967}
2 files changed