master
Use more static imports.
Use `assertThrows` more.
Add HttpHeaders constants for on-prefetch-activation.
Address some more counterfactual [CheckedExceptionNotThrown](https://errorprone.info/bugpattern/CheckedExceptionNotThrown) findings.
Use yet more static imports.
Rename the remaining `PackageSanityTests` (plural) classes to "`PackageSanityTest`" (singular).
Use JUnit's `assertThrows` instead of ours.
Address nullness-checking errors in tests.
Migrate off `assertSame` and `assertNotSame` and onto Truth.