[ThreadPool] Fix docs to match new API

R=etiennep@chromium.org

Bug: 1026641
Change-Id: I68c6e40f080ac5808cd9c67e227695ca921e1691
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2026714
Auto-Submit: Gabriel Charette <gab@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736281}

docs/threading_and_tasks.md

@@ -654,8 +654,7 @@ void WorkerTask(base::JobDelegate* job_delegate) {
 // Returns the latest thread-safe number of incomplete work items.
 void NumIncompleteWorkItems();
 
-base::PostJob(FROM_HERE,
-              {base::ThreadPool()},
+base::PostJob(FROM_HERE, {},
               base::BindRepeating(&WorkerTask),
               base::BindRepeating(&NumIncompleteWorkItems));
 ```

docs/threading_and_tasks_testing.md

@@ -106,9 +106,8 @@ class FooService {
  public:
   FooService()
       : backend_task_runner_(
-            base::CreateSequencedTaskRunnerWithTraits(
-                base::MayBlock(), base::ThreadPool(),
-                base::TaskPriority::BEST_EFFORT))),
+            base::ThreadPool::CreateSequencedTaskRunner(
+                {base::MayBlock(), base::TaskPriority::BEST_EFFORT})),
         backend_(new FooBackend,
                  base::OnTaskRunnerDeleter(backend_task_runner_)) {}
 
@@ -117,7 +116,7 @@ class FooService {
     DCHECK(owning_sequence_->RunsTasksInCurrentSequence());
     backend_task_runner_->PostTaskAndReply(
         base::BindOnce(&FooBackend::Flush, Unretained(backend_.get()),
-        std::move(on_done));
+        std::move(on_done)));
   }
 
  private:
@@ -254,12 +253,12 @@ TEST(FooTest, TimeoutExceeded)
       base::test::TaskEnvironment::TimeSource::MOCK_TIME};
   base::WaitableEvent event;
   base::RunLoop run_loop;
-  base::PostTaskAndReply(
-      FROM_HERE, {base::ThreadPool(), base::MayBlock()},
+  base::ThreadPool::PostTaskAndReply(
+      FROM_HERE, {base::MayBlock()},
       base::BindOnce(&BlocksOnEvent, base::Unretained(&event)),
       run_loop.QuitClosure());
-  base::PostDelayedTask(
-      FROM_HERE, {base::ThreadPool()},
+  base::ThreadPool::PostDelayedTask(
+      FROM_HERE, {},
       base::BindOnce(&WaitableEvent::Signal, base::Unretained(&event)),
       kTimeout);
   // Can't use task_environment.FastForwardBy() since BlocksOnEvent blocks