Add an API to get active icon for screen saver

In order to improve the clarity of current screen saver, we need to get
the active icon from DreamBackend and add it on the left side of current
screen saver preference.

Bug: 129994275
Test: robotests
Change-Id: I844ccdcdccc270f23f1a0f0f0ce5335fce184c5b
1 file changed