Add methods to check tag availability

setTagUpToDate:
    record the new tag's cookie while creating a tag object, the value
    could be used to check the tag availability

isTagUpToDate:
    compare the latest cookie to the tag's cookie, which generated
    when it was created, to check whether the tag object is the
    latest or not

Bug: 199291025
Test: test with some reader apps, test pass
Merged-In: Ia1e21a95605020b6af8cceda0869f982048568ba
Change-Id: Ia1e21a95605020b6af8cceda0869f982048568ba