replace SkNVRefCnt with SkRefCnt

SkNVRefCnt trades a small amount of code size (vtable) and runtime
(vptr) memory usage for a larger amount of code size (templating).  It
was written back in a time when all we were really thinking about was
runtime memory usage, so I'm curious to see where performance, code
size, and memory usage all move if it's removed.

Looking at the types I've changed here, my guess is that performance and
memory usage will be basically unchanged, and that code size will drop a
bit.  Nothing else it's nicer to have only one ref-counting base class.

Change-Id: I7d56a2b9e2b9fb000ff97792159ea1ff4f5e6f13
Reviewed-on: https://skia-review.googlesource.com/c/166203
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
14 files changed