Spin off just SkLazyFnPtr from 305513002.

src/ports/SkAtomics_sync.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_sync_DEFINED
 #define SkAtomics_sync_DEFINED
 
@@ skipping 14 matching lines @@
 }
 
 static inline __attribute__((always_inline)) void sk_membar_acquire__after_atomic_dec() { }
 
 static inline __attribute__((always_inline)) bool sk_atomic_cas(int32_t* addr,
                                                                 int32_t before,
                                                                 int32_t after) {
     return __sync_bool_compare_and_swap(addr, before, after);
 }
 
+static inline __attribute__((always_inline)) void* sk_atomic_cas(void** addr,
+                                                                 void* before,
+                                                                 void* after) {
+    return __sync_val_compare_and_swap(addr, before, after);
+}
+
 static inline __attribute__((always_inline)) void sk_membar_acquire__after_atomic_conditional_inc() { }
 
 #endif