Abort promises before sending new ones in MediaSearchWidget

Before sending new searches to the API, abort the previous ones if
they were not resolved. This will assure that the result presented
on the screen is valid to the latest search that was done even if
the user types quickly and sends many async requests simultaneously.

Bug: 67438
Change-Id: If88123019bfa972520e9db7c627a7f4cd8fc2526
Merge "Abort promises before sending new ones in MediaSearchWidget"