Add sk_parallel_for()

src/core/SkMultiPictureDraw.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.
  */
 
 // Need to include something before #if SK_SUPPORT_GPU so that the Android
 // framework build, which gets its defines from SkTypes rather than a makefile,
 // has the definition before checking it.
@@ skipping 73 matching lines @@
     ~AutoMPDReset() { fMPD->reset(); }
 };
 
 //#define FORCE_SINGLE_THREAD_DRAWING_FOR_TESTING
 
 void SkMultiPictureDraw::draw(bool flush) {
     AutoMPDReset mpdreset(this);
 
 #ifdef FORCE_SINGLE_THREAD_DRAWING_FOR_TESTING
     for (int i = 0; i < fThreadSafeDrawData.count(); ++i) {
-        DrawData* dd = &fThreadSafeDrawData.begin()[i];
-        dd->fCanvas->drawPicture(dd->fPicture, &dd->fMatrix, dd->fPaint);
+        fThreadSafeDrawData[i].draw();
     }
 #else
-    // we place the taskgroup after the MPDReset, to ensure that we don't delete the DrawData
-    // objects until after we're finished the tasks (which have pointers to the data).
-    SkTaskGroup group;
-    group.batch(DrawData::Draw, fThreadSafeDrawData.begin(), fThreadSafeDrawData.count());
+    sk_parallel_for(fThreadSafeDrawData.count(), [&](int i) {
+        fThreadSafeDrawData[i].draw();
+    });
 #endif
-    // we deliberately don't call wait() here, since the destructor will do that, this allows us
-    // to continue processing gpu-data without having to wait on the cpu tasks.
+
+    // N.B. we could get going on any GPU work from this main thread while the CPU work runs.
+    // But in practice, we've either got GPU work or CPU work, not both.
 
     const int count = fGPUDrawData.count();
     if (0 == count) {
         return;
     }
 
 #if !defined(SK_IGNORE_GPU_LAYER_HOISTING) && SK_SUPPORT_GPU
     GrContext* context = fGPUDrawData[0].fCanvas->getGrContext();
     SkASSERT(context);
 
@@ skipping 84 matching lines @@
 
 #if !defined(SK_IGNORE_GPU_LAYER_HOISTING) && SK_SUPPORT_GPU
     GrLayerHoister::UnlockLayers(context, atlasedNeedRendering);
     GrLayerHoister::UnlockLayers(context, atlasedRecycled);
 #if !GR_CACHE_HOISTED_LAYERS
     GrLayerHoister::PurgeCache(context);
 #endif
 #endif
 }