[Divider] Use window background color for veils while dragging

Use the window background color as the veil color while dragging.
Default color is used only when such info is unavailable, i.e.
cross-process embedding.

Bug: 327067596
Test: atest DividerPresenterTest
Change-Id: I5df34ec754cf5c86240df8d037a0052bb792180d
2 files changed