Don't count things for progress until they *really* start loading

Fonts in particular don't start loading when they are declared, but when they
are first referenced. Don't count fonts toward progress until they are
referenced, since the font will then block progress completion until the load
event if it is never referenced.

BUG=513459

Review-Url: https://codereview.chromium.org/2374903002
Cr-Commit-Position: refs/heads/master@{#421664}
2 files changed