When creating a TaskIdAttributeContainer for a desktop task, creates an
IconView to avoid an NPE when picking a desktop app as the second split
target (see TaskBarUIController#triggerSecondAppForSplit).
Test: Select an app open in Desktop Mode as the second split target.
Bug: 279586624
Change-Id: I1949d923523b6e9e6112b3e909edf1e8d632b3e2