Mobile-data-download need access to android_downloader_lib.
Change access modifier for getContentTag() and getLastModifiedTimeSeconds() to public since we need to access them from MDD package.
This change is needed for adding MDD in AOSP.
Internal has the same changes. CL: 18898499

Test: m
Change-Id: I070e8789ee95d983e7c0a1b99a66988f9a14e790