Add SkNVRefCnt, prune down SkPicture's size

SkNVRefCnt is a variant of SkRefCnt that's Not Virtual, so weighs 4 bytes
instead of 8 or 16.  There's only benefit to doing this if the deriving class
does not otherwise need a vtable, e.g. SkPicture.

I've stripped out some cruft from SkPicture, rearranged fields to pack tightly,
and added compile asserts for the sizes of SkPicture, SkRecord, and
SkVarAlloc.

BUG=skia:3144

Review URL: https://codereview.chromium.org/741793002

1 files changed, 1 insertions, 0 deletions

diff --git a/src/core/SkVarAlloc.h b/src/core/SkVarAlloc.h
index 9eac658828..2e8f19c8fe 100644
--- a/src/core/SkVarAlloc.h
+++ b/src/core/SkVarAlloc.h
@@ -37,5 +37,6 @@ private:
     struct Block;
     Block* fBlock;
 };
+SK_COMPILE_ASSERT(sizeof(SkVarAlloc) <= 24, SkVarAllocSize);
 
 #endif//SkVarAlloc_DEFINED