@Override
    public Set<String> consumeProperties(Context context) {
      if (context.properties().containsKey("dizzle")) {
        return ImmutableSet.of("dizzle");
      } else {
        return Collections.emptySet();
      }
    }
Tests that extensions providing their own implemented annotation types or options get picked
up.
value/src/test/java/com/google/auto/value/processor/ExtensionTest.java