Move texture proxy allocation for atlas to constructor.

This is to set up for allocating additional texture proxies as needed.

Change-Id: Ibc0480c30d8efd6ccf8278f6dbdd3bfa3ee2397d
Reviewed-on: https://skia-review.googlesource.com/41744
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed