Dash - 'default' scope icons in the Dash bottom nav bar should not be displayed if their 'default view' is empty.

The 'default' scope icons in the Dash bottom nav bar (Music, Video, Messages, Photos, Apps, Files) should not be displayed if their 'default view' is empty ('default view' is the content displayed before the user performs a search, e.g. the results of a null search).

The means that for example the 'Messages' icon should not appear if the Messages scope is not connected to any message services. Or the 'Photo' icon should not appear if the user has no photos, either stored locally or accessed via an online photos service.

Note that the Apps and Files icons would always pass this test, irrespective of internet connectivity, so we probably only need to test the Photos, Messages, Music and Videos default scopes.

If a default scope fails this test, pressing the keyboard shortcut to jump direct to that scope should perform no action. Ideally the keyboard shortcut overlay should become dynamic and only display keyboard shortcuts to the default scopes that are currently active, however if it is not possible to do this in 13.04 it can wait until 13.10.

The design rational for this is that we want Ubuntu to adapt to our user's needs. We have already implemented 'adaptive' functionality into the indicators, for example if you don't have email set up via either Thunderbird or a WebApp the Messaging menu won't display email options. The rule we are trying to implement is "only display options that serve a purpose to the specific user".

--------------- Option 1 ---------------

Desired resolution:

- Perform a null search (e.g. try to retrieve the default view) on the Music, Video, Message and Photo default scopes. If any of the Music, Video, Message and Photo searches do not return any results, the icon for these default scopes should not appear in the Dash bottom nav bar.

- Note the search does not need to retrieve the images, it only needs to try to retrieve a single result from each default master scope. This is because as long as any one of the scopes supplying these default master scopes returns a single result, the icon for that default master scope can be displayed in the Dash bottom nav bar. Therefore the search of each default master scope ccould be terminated as soon as the first result arrives.

- This search should be triggered by the following events:

  1) 30 seconds after booting into the desktop or when the user first opens the Dash, whichever comes first.

  2) whenever internet connection is lost

  3) whenever internet connection is gained

  4) when an external app or service requests that the search is re-run. For example a future version of the Online Accounts service may wish to request that this search is re-run whenever the user adds or removes account credentials

  5) when the user presses the F5 key while the Dash is open

--------------- Option 2 ---------------

Desired resolution:

- When a user installs Ubuntu 13.04 the Music, Video, Messages, and Photos icons should not be displayed in the Dash bottom nav.

- Every time the user opens the Dash, a null search of the Music, Video, Messages, and Photos master scopes is performed in parallel (e.g. the opening of the Dash is not delayed to wait for the results from the search). A possible alternative would be to search the Music, Video, Messages, and Photos master scopes whenever a search in the Dash Home is performed, however performing a null search would be better if this is possible.

- If any of these four master scopes deliver >0 results, their icon is either
    a) faded in to the Dash bottom bar
    b) or if this is not possible in 13.04, it appears the next time the user opens
       the dash

- Once an icon appears, it becomes 'fixed' to the Dash bottom nav and no longer needs to be searched.