Set activity background color for screenshot consistency.

Fix: 328065246
Bug: 324288919
Bug: 305193969
Test: atest CtsInputTestCases:PointerIconTest
Test: v2/android-virtual-infra/test_mapping/presubmit-avd
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:7c98dd6815e55ad2576de3db10e796d4a46df27e)
Merged-In: I725f3ec06f9381501680f04ceafb694b0bc4a78f
Change-Id: I725f3ec06f9381501680f04ceafb694b0bc4a78f
4 files changed