Fix check for valid proxies returned by AtlasManager.

Also renames a lot of variables to make it clearer that getProxies()
returns the number of instantiated proxies, not the number of all
proxies.

Bug: skia:
Change-Id: Ifbc910cbd6635dccdb4e7f0df2e69a0f341130af
Reviewed-on: https://skia-review.googlesource.com/128660
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
7 files changed