Activity can be used only in two cases.
1) Calling uid matches uid grantee.
2) Calling uid is is system. This flow is used by getToken methods with
notifyAuthFailure=true.
Test: Existing CTS tests
Bug: 158480899
Merged-In: I1421c333b6cebb4f7cddcdd8766298f6872e933b
Change-Id: I18af48cf3cb4ad23a3e5b02a8ea1416aa5570dba