Open was not calling through to upstream.open. This was not problematic for
reading, because DataSourceInputStream.read would open the upstream if it's
not open already. It was however a problem for calling getUri() between
calling open and the first call to read, which would end up calling
upstream.getUri() on the not-yet-opened upstream.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=195689472
