[Cros SR] Provide the app shortcut SP with access to Roselle.

See here for context:

  https://docs.google.com/document/d/1GTQ3vvrszK4I1pDzmTFb6krmUzAXox0V9ZIqIi_GH1E/edit?usp=sharing

We are expanding Roselle to re-rank the results returned when the user enters
a query. However, these results include Arc app shortcuts as well as apps
themselves, so they need to be ranked. This CL gives the shortcut search
provider access to the Roselle model, for future use in training/ranking.

Bug: 931149
Change-Id: I826be986a98d870de21ecd9c88f5a266c5d0308e
Reviewed-on: https://chromium-review.googlesource.com/c/1478570
Commit-Queue: Tony Yeoman <tby@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634428}
9 files changed