GitLab

- Deletes BookmarkContextBar files and usage from BookmarkHomeVC.
- Uses BookmarkHomeVC navigationController UIToolbar instead.
- Creates accessibilityIdentifiers for toolbar buttons.
- Changes the BookmarkTableCell margins since these were giving the effect of shrinking row height.

Screenshots
Old: https://drive.google.com/open?id=1v3GQRiiPiIzJNZ7Lxd-pgpaaqP15b0PR
New: https://drive.google.com/open?id=1z5mOT3p1NBj62EaMKfR2P5WSD2irQmyX

Bug: 839435
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I155365b6f9520010153ce97187ef1f6a2a8514f7
Reviewed-on: https://chromium-review.googlesource.com/1054123
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558114}