Style Change: NULL->nullptr

src/lazy/SkDiscardableMemoryPool.h

Index: src/lazy/SkDiscardableMemoryPool.h
diff --git a/src/lazy/SkDiscardableMemoryPool.h b/src/lazy/SkDiscardableMemoryPool.h
index 33c176d3f2b51da8be9bc3ad1b814fcce6be667b..92ba48bcb492fb3f50bd50ea2143ad5016fbc676 100644
--- a/src/lazy/SkDiscardableMemoryPool.h
+++ b/src/lazy/SkDiscardableMemoryPool.h
@@ -53,7 +53,7 @@ public:
      *  Without mutex, will be not be thread safe.
      */
     static SkDiscardableMemoryPool* Create(
-            size_t size, SkBaseMutex* mutex = NULL);
+            size_t size, SkBaseMutex* mutex = nullptr);
 };
 
 /**