Use destructors to free resources owned by lazy proxy callbacks

Change-Id: I103355f12e808c636803491c86d3c887113f088c
Reviewed-on: https://skia-review.googlesource.com/c/192541
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
7 files changed