[NTP] Merge the context menu code for NTP tiles and suggestions
Adds a ContextMenuHandler class that takes care of creating the
menu and triages the item clicks, allowing to remove that from
the NTPManager and the Snippet ViewHolder.
Also adds the possibility to disable touch on the legacy ScrollView,
so that we can disable scrolling while the context menu is shown.
BUG=
651045
Committed:
https://crrev.com/99f920d4c9724872f6176b9c71eb7b198ed3b9ea
Cr-Commit-Position: refs/heads/master@{#427669}