SkOnce: let f be any functor, update comments

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 "SkThreadPool.h"
 #include "Test.h"
@@ skipping 10 matching lines @@
     // No matter how many times we do this, x will be 5.
     SkOnce(&once, add_five, &x);
     SkOnce(&once, add_five, &x);
     SkOnce(&once, add_five, &x);
     SkOnce(&once, add_five, &x);
     SkOnce(&once, add_five, &x);
 
     REPORTER_ASSERT(r, 5 == x);
 }
 
+struct AddFour { void operator()(int* x) { *x += 4; } };
+
+DEF_TEST(SkOnce_MiscFeatures, r) {
+    // Tests that we support functors and explicit SkOnceFlags.
+    int x = 0;
+
+    SkOnceFlag once = SK_ONCE_INIT;
+    SkOnce(&once, AddFour(), &x);
+    SkOnce(&once, AddFour(), &x);
+    SkOnce(&once, AddFour(), &x);
+
+    REPORTER_ASSERT(r, 4 == x);
+}
+
 static void add_six(int* x) {
     *x += 6;
 }
 
 class Racer : public SkRunnable {
 public:
     SkOnceFlag* once;
     int* ptr;
 
     virtual void run() SK_OVERRIDE {
@@ skipping 16 matching lines @@
     // Let them race.
     SkThreadPool pool(kThreads);
     for (int i = 0; i < kTasks; i++) {
         pool.add(&racers[i]);
     }
     pool.wait();
 
     // Only one should have done the +=.
     REPORTER_ASSERT(r, 6 == x);
 }