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