
Currently we default to assuming the cache is up-to-date. This is likely wrong. Normal web servers provide Last Modified for files they serve. If it is absent, chances are high the image is served by some sort of a dynamic service, which may modify the URL on fly. In any case, always updating the image is a safer choice. Change-Id: I0548db14a97638d26ebb687e8f47f1b295d1f774