Revert of SkThreadPool ~~> SkTaskGroup

tools/flags/SkCommonFlags.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 "SkCommonFlags.h"
+#include "SkThreadPool.h"
 
 DEFINE_string(config, "565 8888 pdf gpu nonrendering angle",
               "Options: 565 8888 pdf gpu nonrendering msaa4 msaa16 nvprmsaa4 nvprmsaa16 "
               "gpunull gpudebug angle mesa");
 
 DEFINE_bool(cpu, true, "master switch for running CPU-bound work.");
 
 DEFINE_bool(dryRun, false,
             "just print the tests that would be run, without actually running them.");
 
@@ skipping 15 matching lines @@
                "^ and $ requires an exact match\n"
                "If a GM does not match any list entry,\n"
                "it is skipped unless some list entry starts with ~");
 
 DEFINE_bool2(quiet, q, false, "if true, don't print status updates.");
 
 DEFINE_bool(resetGpuContext, true, "Reset the GrContext before running each test.");
 DEFINE_bool(abandonGpuContext, false, "Abandon the GrContext after running each test. "
                                       "Implies --resetGpuContext.");
 
+DEFINE_bool2(single, z, false, "run tests on a single thread internally.");
+
 DEFINE_string(skps, "skps", "Directory to read skps from.");
 
-DEFINE_int32(threads, 0, "Run threadsafe tests on a threadpool with this many threads, "
-                         "defaulting to one thread per core.");
+DEFINE_int32(threads, SkThreadPool::kThreadPerCore,
+             "run threadsafe tests on a threadpool with this many threads.");
 
 DEFINE_bool2(verbose, v, false, "enable verbose output from the test driver.");
 
 DEFINE_bool2(veryVerbose, V, false, "tell individual tests to be verbose.");
 
 DEFINE_string2(writePath, w, "", "If set, write bitmaps here as .pngs.");