This CL refactors some methods in OverviewTask to rely on OverviewSplitTask. It also changes the BaseOverview getTasks function to retrieve the parent task and support cases where only the bottomright_snapshot is available in the recent tasks.
Bug: 320633351
Test: TaplTestsSplitscreen
Flag: N/A
Change-Id: I226f895810ce3b46cc107f76cd85e2918abf7088