Add sk_parallel_for()

tests/PathOpsThreadedCommon.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "PathOpsExtendedTest.h"
 #include "PathOpsThreadedCommon.h"
 #include "SkTaskGroup.h"
 
 PathOpsThreadedTestRunner::~PathOpsThreadedTestRunner() {
     for (int index = 0; index < fRunnables.count(); index++) {
         SkDELETE(fRunnables[index]);
     }
 }
 
 void PathOpsThreadedTestRunner::render() {
-    SkTaskGroup tg;
-    for (int index = 0; index < fRunnables.count(); ++ index) {
-        tg.add(fRunnables[index]);
-    }
+    sk_parallel_for(fRunnables.count(), [&](int i) {
+        fRunnables[i]->run();
+    });
 }