Querying an icon will have another stage (fetching from the Google favicon server) that can take quite some time. I need to figure out what the UI should display in the mean-time.

Possibilities:
 1. more updates:
    - no icon, initially
    - show default icon / colored tile after we find out the icon is missing in the local cache
    - show the real icon after we fetch it from the server

 2. blank -> final (possibly a long delay) 
   - no icon, initially
   - replace with real icon / fallback icon after we get all info (from local cache / Google server)

 3. gray fallback -> final (possible flicker)
   - gray fallback icon / default icon initially,
   - replace with real icon / fallback icon after we get all info (from local cache / Google server)



For reference: current behaviour:
   1. in snippet's publishers:
     - initially, the space for the favicon is blank
     - we check local cache 
        -> if we have the icon, we show it, 
        -> otherwise we show the default "blank-page" icon and initiate a fetch from a Google server
     - if we get a result from the Google server, we replace the blank icon for the fetched on

  2. in NTP tiles:
   - initially, the tile is blank
   - we check local cache
     -> if we have the icon, we show it,
     -> otherwise, we show the fallback colored/gray icon