rebaseline_server live queries: allow comparison against summary files within the Skia repo

This is a step towards providing SKP comparisons against expectations, not just
other actual results... we still need to allow the user to select
JSONKEY_EXPECTEDRESULTS vs JSONKEY_ACTUALRESULTS within the summary
files found.

BUG=skia:1942
NOTREECHECKS=true
NOTRY=true
R=rmistry@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/442203002
5 files changed