Set assist settings and tweak tests to align with platform expectations.

Change assumptions for screenshot to rely on context setting, set assist
settings rather than checking for them, and modify DisableContextTest to
change settings within the test method so subsequent tests are not
affected by failure.

Bug: 23240210
Bug: 23235045
Change-Id: I4912ee5384434efa1279e4f0b38d4b6653468d68
4 files changed