Implement sk_atomic_conditional_inc with sk_atomic_cas.

src/ports/SkAtomics_win.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_win_DEFINED
 #define SkAtomics_win_DEFINED
 
@@ skipping 18 matching lines @@
     return _InterlockedExchangeAdd(reinterpret_cast<long*>(addr), static_cast<long>(inc));
 }
 
 static inline int32_t sk_atomic_dec(int32_t* addr) {
     // InterlockedDecrement returns the new value, we want to return the old.
     return _InterlockedDecrement(reinterpret_cast<long*>(addr)) + 1;
 }
 
 static inline void sk_membar_acquire__after_atomic_dec() { }
 
-static inline int32_t sk_atomic_conditional_inc(int32_t* addr) {
-    long value = *addr;
-    while (true) {
-        if (value == 0) {
-            return 0;
-        }
-
-        long before = _InterlockedCompareExchange(reinterpret_cast<long*>(addr), value + 1, value);
-
-        if (before == value) {
-            return value;
-        } else {
-            value = before;
-        }
-    }
-}
-
 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_membar_acquire__after_atomic_conditional_inc() { }
 
 #endif