adjust prefetch URL we hit in UploadRenderedSKPs, and display view URL in CompareRenderedSKPs

This goes along with https://codereview.chromium.org/453433004/
('rebaseline_server: allow live queries to examine JSONKEY_EXPECTEDRESULTS
or JSONKEY_ACTUALRESULTS')

For full context, see https://goto.google.com/CorrectnessTestingBigIssues

BUG=skia:1942
R=borenet@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/446373003