Turn on MPD threading in nanobench.

bench/nanobench.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 <ctype.h>
 
 #include "Benchmark.h"
@@ skipping 582 matching lines @@
     int fCurrentRecording;
     int fCurrentScale;
     int fCurrentSKP;
     int fCurrentUseMPD;
 };
 
 int nanobench_main();
 int nanobench_main() {
     SetupCrashHandler();
     SkAutoGraphics ag;
-    // Multithreading is disabled pending resolution of skia:3149
-    //SkTaskGroup::Enabler enabled;
+    SkTaskGroup::Enabler enabled;
 
 #if SK_SUPPORT_GPU
     GrContext::Options grContextOpts;
     grContextOpts.fDrawPathToCompressedTexture = FLAGS_gpuCompressAlphaMasks;
     gGrFactory.reset(SkNEW_ARGS(GrContextFactory, (grContextOpts)));
 #endif
 
     if (FLAGS_veryVerbose) {
         FLAGS_verbose = true;
     }
@@ skipping 172 matching lines @@
 
     return 0;
 }
 
 #if !defined SK_BUILD_FOR_IOS
 int main(int argc, char** argv) {
     SkCommandLineFlags::Parse(argc, argv);
     return nanobench_main();
 }
 #endif