Implement sk_atomic_conditional_inc with sk_atomic_cas.

src/ports/SkAtomics_none.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkAtomics_none_DEFINED
 #define SkAtomics_none_DEFINED
 
@@ skipping 14 matching lines @@
 }
 
 static inline int32_t sk_atomic_dec(int32_t* addr) {
     int32_t value = *addr;
     *addr = value - 1;
     return value;
 }
 
 static inline void sk_membar_acquire__after_atomic_dec() { }
 
-static inline int32_t sk_atomic_conditional_inc(int32_t* addr) {
-    int32_t value = *addr;
-    if (value != 0) ++*addr;
-    return value;
-}
-
 static inline bool sk_atomic_cas(int32_t* addr, int32_t before, int32_t after) {
     if (*addr != before) return false;
     *addr = after;
     return true;
 }
 
 static inline void sk_membar_acquire__after_atomic_conditional_inc() { }
 
 #endif