Fix memory leak in iOS viewer.

Forgot to add code to drain the Autorelease pool, so objects created
with autorelease just built up over time.

Bug: skia:8243
Change-Id: I373c6820df8ee102b110386377378858c235b2fa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/252601
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed