Modernize and trim down SkOnce.

tests/OnceTest.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 "SkOnce.h"
 #include "SkTaskGroup.h"
 #include "Test.h"
 
 static void add_five(int* x) {
     *x += 5;
 }
 
-SK_DECLARE_STATIC_ONCE(st_once);
 DEF_TEST(SkOnce_Singlethreaded, r) {
     int x = 0;
 
     // No matter how many times we do this, x will be 5.
-    SkOnce(&st_once, add_five, &x);
-    SkOnce(&st_once, add_five, &x);
-    SkOnce(&st_once, add_five, &x);
-    SkOnce(&st_once, add_five, &x);
-    SkOnce(&st_once, add_five, &x);
+    SkOnce once;
+    once(add_five, &x);
+    once(add_five, &x);
+    once(add_five, &x);
+    once(add_five, &x);
+    once(add_five, &x);
 
     REPORTER_ASSERT(r, 5 == x);
 }
 
-SK_DECLARE_STATIC_ONCE(mt_once);
 DEF_TEST(SkOnce_Multithreaded, r) {
     int x = 0;
+
     // Run a bunch of tasks to be the first to add six to x.
+    SkOnce once;
     SkTaskGroup().batch(1021, [&](int) {
-        void(*add_six)(int*) = [](int* p) { *p += 6; };
-        SkOnce(&mt_once, add_six, &x);
+        once([&] { x += 6; });
     });
 
     // Only one should have done the +=.
     REPORTER_ASSERT(r, 6 == x);
 }
 
 static int gX = 0;
 static void inc_gX() { gX++; }
 
-SK_DECLARE_STATIC_ONCE(noarg_once);
 DEF_TEST(SkOnce_NoArg, r) {
-    SkOnce(&noarg_once, inc_gX);
-    SkOnce(&noarg_once, inc_gX);
-    SkOnce(&noarg_once, inc_gX);
+    SkOnce once;
+    once(inc_gX);
+    once(inc_gX);
+    once(inc_gX);
     REPORTER_ASSERT(r, 1 == gX);
 }