[EoS] Adds requests for category images.

* If no catalog is present, requests one from the network and displays
  default images.  When request finishes, updates the category images.
* Updates category images right away if not requesting from the network.
* Fixes the query in GetCatalogTask so that if there is no "current"
  catalog, it will use the "downloading" catalog instead.

Bug: 867488
Change-Id: Ic307f77a4b3ae2ededa711f619059b1aed562012
Reviewed-on: https://chromium-review.googlesource.com/1252908
Commit-Queue: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Cathy Li <chili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595605}
6 files changed