While we can, restrict SkFixedAlloc/SkFallbackAlloc to POD.

This trims the overhead down to a uniform 4 bytes.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4786

Change-Id: I92127a0c2d6c23a4a372eca39842e22195d2dc99
Reviewed-on: https://skia-review.googlesource.com/4786
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
5 files changed