Revert "Dont update thumbnails of freeform windows on focus change"

This reverts commit 17690ffcf7ed47b2719c65bb148190ddcdf4232c.

Can not reproduce the problem reported in the original bug that
required the reverted CL.

Bug: 23591449
Bug: 23562904
Change-Id: I8262cef52036816e9b3f422f6b75b1959a4da7cd
2 files changed