Revert of SkOncePtr -> SkOnce

tests/OncePtrTest.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Test.h"
+#include "SkOncePtr.h"
+#include "SkTaskGroup.h"
+
+SK_DECLARE_STATIC_ONCE_PTR(int, once);
+
+DEF_TEST(OncePtr, r) {
+    static SkAtomic<int> calls(0);
+    auto create = [&] {
+        calls.fetch_add(1);
+        return new int(5);
+    };
+
+    SkTaskGroup().batch(sk_num_cores()*4, [&](size_t) {
+        int* n = once.get(create);
+        REPORTER_ASSERT(r, *n == 5);
+    });
+    REPORTER_ASSERT(r, calls.load() == 1);
+}