Reland of SkOncePtr -> SkOnce

src/core/SkPathRef.cpp

Index: src/core/SkPathRef.cpp
diff --git a/src/core/SkPathRef.cpp b/src/core/SkPathRef.cpp
index b18055136f54ce2cc1ed95ed7fb569c298ec0c4d..2fc2de935c149031342cdcdc538535bf50dcb49b 100644
--- a/src/core/SkPathRef.cpp
+++ b/src/core/SkPathRef.cpp
@@ -6,7 +6,7 @@
  */
 
 #include "SkBuffer.h"
-#include "SkOncePtr.h"
+#include "SkOnce.h"
 #include "SkPath.h"
 #include "SkPathRef.h"
 #include <limits>
@@ -45,13 +45,15 @@
     SkDEBUGCODE(fEditorsAttached = 0x7777777;)
 }
 
-SK_DECLARE_STATIC_ONCE_PTR(SkPathRef, empty);
+static SkPathRef* gEmpty = nullptr;
+
 SkPathRef* SkPathRef::CreateEmpty() {
-    return SkRef(empty.get([]{
-        SkPathRef* pr = new SkPathRef;
-        pr->computeBounds();   // Avoids races later to be the first to do this.
-        return pr;
-    }));
+    static SkOnce once;
+    once([]{
+        gEmpty = new SkPathRef;
+        gEmpty->computeBounds();   // Avoids races later to be the first to do this.
+    });
+    return SkRef(gEmpty);
 }
 
 void SkPathRef::CreateTransformedCopy(SkAutoTUnref<SkPathRef>* dst,
@@ -469,7 +471,7 @@
 }
 
 void SkPathRef::addGenIDChangeListener(GenIDChangeListener* listener) {
-    if (nullptr == listener || this == (SkPathRef*)empty) {
+    if (nullptr == listener || this == gEmpty) {
         delete listener;
         return;
     }