Experiment of three translate bubble UI options

This change introduces two new desktop UI options - TAB and BUTTON_GM2,
to translate bubble for experimentation. The flags has been added to chrome://flags.
Implementation for TAB and BUTTON_GM2 are in progress.
Default is set to existing BUTTON option.
Note that TAB option has been released on IOS and Android.

Change-Id: Icc79269c4364b431797ef3635b773ad5e2ad7fc4
Bug: 963148
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610567
Commit-Queue: Haohao Wang <hhw@google.com>
Reviewed-by: anthonyvd <anthonyvd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661182}
9 files changed