Fix tasks not resized in split-screen

With 465b1e18, only root tasks are allowed to be organized. Therefore,
the direct children of organized tasks are no longer evaluated as
organized.

Do not set bounds to the children of organized tasks, and just follow
organized tasks to resize accordingly.

Bug: 152619437
Test: drag divider in split-screen
Change-Id: Icf84d3817b8cd506af49e54475f78eb001319d78