Revert of SkOncePtr -> SkOnce

src/lazy/SkDiscardableMemoryPool.cpp

Index: src/lazy/SkDiscardableMemoryPool.cpp
diff --git a/src/lazy/SkDiscardableMemoryPool.cpp b/src/lazy/SkDiscardableMemoryPool.cpp
index d6753def9d2263e84bc8d156c0e317616b5d4025..2be4c755f1e0c3196fbc13a439333c7cdeadd55f 100644
--- a/src/lazy/SkDiscardableMemoryPool.cpp
+++ b/src/lazy/SkDiscardableMemoryPool.cpp
@@ -9,7 +9,7 @@
 #include "SkDiscardableMemoryPool.h"
 #include "SkImageGenerator.h"
 #include "SkMutex.h"
-#include "SkOnce.h"
+#include "SkOncePtr.h"
 #include "SkTInternalLList.h"
 
 // Note:
@@ -245,13 +245,11 @@
 }
 
 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;
-}
+}