Add an API to update the remote view secondary toolbar in custom tabs

This is the session level counterpart of
CustomTabsIntent.Builder.setSecondaryToolbarViews for updating an
existing secondary toolbar with a new RemoteView. The RemoteView can be
null in which case the current secondary toolbar is dismissed.

BUG=27970505

Change-Id: I3c085a3a3f461bda54d8d9f5e220c7a87722450d
2 files changed