Revert of SkOncePtr -> SkOnce

src/lazy/SkDiscardableMemoryPool.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDiscardableMemory.h"
 #include "SkDiscardableMemoryPool.h"
 #include "SkImageGenerator.h"
 #include "SkMutex.h"
-#include "SkOnce.h"
+#include "SkOncePtr.h"
 #include "SkTInternalLList.h"
 
 // Note:
 // A PoolDiscardableMemory is memory that is counted in a pool.
 // A DiscardableMemoryPool is a pool of PoolDiscardableMemorys.
 
 namespace {
 
 class PoolDiscardableMemory;
 
@@ skipping 215 matching lines @@
     this->dumpDownTo(0);
 }
 
 }  // namespace
 
 SkDiscardableMemoryPool* SkDiscardableMemoryPool::Create(size_t size, SkMutex* mutex) {
     return new DiscardableMemoryPool(size, mutex);
 }
 
 SK_DECLARE_STATIC_MUTEX(gMutex);
+SK_DECLARE_STATIC_ONCE_PTR(SkDiscardableMemoryPool, global);
 
 SkDiscardableMemoryPool* SkGetGlobalDiscardableMemoryPool() {
-    static SkOnce once;
-    static SkDiscardableMemoryPool* global;
-    once([]{
-        global = SkDiscardableMemoryPool::Create(SK_DEFAULT_GLOBAL_DISCARDABLE_MEMORY_POOL_SIZE,
-                                                 &gMutex);
+    return global.get([] {
+        return SkDiscardableMemoryPool::Create(SK_DEFAULT_GLOBAL_DISCARDABLE_MEMORY_POOL_SIZE,
+                                               &gMutex);
     });
-    return global;
 }