Spin off just SkLazyFnPtr from 305513002.

src/ports/SkAtomics_win.h

Index: src/ports/SkAtomics_win.h
diff --git a/src/ports/SkAtomics_win.h b/src/ports/SkAtomics_win.h
index 7454d66055157c347c533eb0430f787d87e7352a..16923947ef0bbb3268175fbc526fc2b64338e5f6 100644
--- a/src/ports/SkAtomics_win.h
+++ b/src/ports/SkAtomics_win.h
@@ -40,6 +40,10 @@ static inline bool sk_atomic_cas(int32_t* addr, int32_t before, int32_t after) {
     return _InterlockedCompareExchange(reinterpret_cast<long*>(addr), after, before) == before;
 }
 
+static inline void* sk_atomic_cas(void** addr, void* before, void* after) {
+    return InterlockedCompareExchangePointer(addr, after, before);
+}
+
 static inline void sk_membar_acquire__after_atomic_conditional_inc() { }
 
 #endif