SkDescriptors to be held in unique_ptr.

This also removes the class operator new override along with
directly calling malloc in SkData, since it has a similar requirements.

CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Debug-ASAN-Trybot;master.client.skia:Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Debug-MSAN-Trybot

Change-Id: Ic68aacf2028d6964d9735a55558862afc9edd19b
Reviewed-on: https://skia-review.googlesource.com/3541
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
6 files changed