Add histograms about hub and spoke navigation usage

This CL adds logging for the following UMA histogram:
1. Tabs.Tasks.HubAndSpokeNavigationUsage.FromDefaultSearchEngine
2. Tabs.Tasks.HubAndSpokeNavigationUsage.FromFormSubmit
3. Tabs.Tasks.HubAndSpokeNavigationUsage.FromOthers

Bug: 856253
Change-Id: I2a83b0e4840c2435802815b3718a65155451d7a6
Reviewed-on: https://chromium-review.googlesource.com/1117834
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Mei Liang <meiliang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576603}
8 files changed