Revert of SkThreadPool ~~> SkTaskGroup (patchset #4 id:60001 of https://codereview.chromium.org/531653002/)

Reason for revert:
Leaks, leaks, leaks.

Original issue's description:
> SkThreadPool ~~> SkTaskGroup
>
> SkTaskGroup is like SkThreadPool except the threads stay in
> one global pool.  Each SkTaskGroup itself is tiny (4 bytes)
> and its wait() method applies only to tasks add()ed to that
> instance, not the whole thread pool.
>
> This means we don't need to bring up new thread pools when
> tests themselves want to use multithreading (e.g. pathops,
> quilt).  We just create a new SkTaskGroup and wait for that
> to complete.  This should be more efficient, and allow us
> to expand where we use threads to really latency sensitive
> places.  E.g. we can probably now use these in nanobench
> for CPU .skp rendering.
>
> Now that all threads are sharing the same pool, I think we
> can remove most of the custom mechanism pathops tests use
> to control threading.  They'll just ride on the global pool
> with all other tests now.
>
> This (temporarily?) removes the GPU multithreading feature
> from DM, which we don't use.
>
> On my desktop, DM runs a little faster (57s -> 55s) in
> Debug, and a lot faster in Release (36s -> 24s).  The bots
> show speedups of similar proportions, cutting more than a
> minute off the N4/Release and Win7/Debug runtimes.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/9c7207b5dc71dc5a96a2eb107d401133333d5b6f

R=caryclark@google.com, bsalomon@google.com, bungeman@google.com, reed@google.com, mtklein@chromium.org
TBR=bsalomon@google.com, bungeman@google.com, caryclark@google.com, mtklein@chromium.org, reed@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/533393002

1 files changed, 5 insertions, 5 deletions

diff --git a/tests/OnceTest.cpp b/tests/OnceTest.cpp
index 192abaaee3..389d257b73 100644
--- a/tests/OnceTest.cpp
+++ b/tests/OnceTest.cpp
@@ -6,7 +6,7 @@
  */
 
 #include "SkOnce.h"
-#include "SkTaskGroup.h"
+#include "SkThreadPool.h"
 #include "Test.h"
 
 static void add_five(int* x) {
@@ -42,7 +42,7 @@ public:
 };
 
 DEF_TEST(SkOnce_Multithreaded, r) {
-    const int kTasks = 16;
+    const int kTasks = 16, kThreads = 4;
 
     // Make a bunch of tasks that will race to be the first to add six to x.
     Racer racers[kTasks];
@@ -54,11 +54,11 @@ DEF_TEST(SkOnce_Multithreaded, r) {
     }
 
     // Let them race.
-    SkTaskGroup tg;
+    SkThreadPool pool(kThreads);
     for (int i = 0; i < kTasks; i++) {
-        tg.add(&racers[i]);
+        pool.add(&racers[i]);
     }
-    tg.wait();
+    pool.wait();
 
     // Only one should have done the +=.
     REPORTER_ASSERT(r, 6 == x);