Photo aggregation logic update.

In the new logic, we'll pick the largest photo (in pixels, using file
size as a tiebreaker for display photos) to determine photo priority
if no super-primary is defined.

If this logic doesn't pick a winner, we fall back to the old photo
priority based on the account.

Change-Id: I9cf58b86a6c22bcf671a4852606a4534fa0fa7da
7 files changed