Modernize and trim down SkOnce.

src/gpu/GrProgramElement.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrProgramElement.h"
 #include "GrGpuResourceRef.h"
+#include "SkAtomics.h"
 
 uint32_t GrProgramElement::CreateUniqueID() {
     static int32_t gUniqueID = SK_InvalidUniqueID;
     uint32_t id;
     do {
         id = static_cast<uint32_t>(sk_atomic_inc(&gUniqueID) + 1);
     } while (id == SK_InvalidUniqueID);
     return id;
 }
 
 void GrProgramElement::addPendingIOs() const {
     for (int i = 0; i < fGpuResources.count(); ++i) {
         fGpuResources[i]->markPendingIO();
     }
 }
 
 void GrProgramElement::removeRefs() const {
     for (int i = 0; i < fGpuResources.count(); ++i) {
         fGpuResources[i]->removeRef();
     }
 }
 
 void GrProgramElement::pendingIOComplete() const {
     for (int i = 0; i < fGpuResources.count(); ++i) {
         fGpuResources[i]->pendingIOComplete();
     }
 }