Migrate off base::ThreadPool()-as-a-trait in /net

This CL is a logical no-op.

It manually covers the use cases the script
(https://crbug.com/1026641#c22) didn't cover in
https://chromium-review.googlesource.com/c/chromium/src/+/2026350.

A few of the affected files were also migrated to
content::GetUIThreadTaskRunner() whenever surrounding code consistency
was at stake (but the bulk of that migration is staged to happen after
this one so this wasn't a priority in this batch).

Most files intentionally kept base/task/post_task.h as an include. It is
still required because of a cyclical dependency during the migration
preventing base/task/thread_pool.h from implicitly providing
base/task/task_traits.h to its users (callers that explicitly store
TaskTraits and include task_traits.h don't have this problem). The
post_task.h include will be cleaned up in a later phase.

This CL was uploaded by git cl split.

R=eroman@chromium.org

Bug: 1026641
Change-Id: Ia43880f3554e081f04e3835238db6fa792f599e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2078662
Commit-Queue: Gabriel Charette <gab@chromium.org>
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745519}

net/base/prioritized_task_runner_unittest.cc

@@ -19,6 +19,7 @@
 #include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/task/post_task.h"
+#include "base/task/thread_pool.h"
 #include "base/test/task_environment.h"
 #include "base/threading/thread_restrictions.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -106,8 +107,7 @@ class PrioritizedTaskRunnerTest : public testing::Test {
 };
 
 TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyThreadCheck) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 
@@ -131,8 +131,7 @@ TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyThreadCheck) {
 }
 
 TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyRunsBothTasks) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 
@@ -150,8 +149,7 @@ TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyRunsBothTasks) {
 }
 
 TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyTestPriority) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 
@@ -191,8 +189,7 @@ TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyTestPriority) {
 
 // Ensure that replies are run in priority order.
 TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyTestReplyPriority) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 
@@ -238,8 +235,7 @@ TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyTestReplyPriority) {
 }
 
 TEST_F(PrioritizedTaskRunnerTest, PriorityOverflow) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 
@@ -282,8 +278,7 @@ TEST_F(PrioritizedTaskRunnerTest, PriorityOverflow) {
 }
 
 TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyWithResultRunsBothTasks) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 
@@ -301,8 +296,7 @@ TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyWithResultRunsBothTasks) {
 }
 
 TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyWithResultTestPriority) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 
@@ -340,8 +334,7 @@ TEST_F(PrioritizedTaskRunnerTest, PostTaskAndReplyWithResultTestPriority) {
 }
 
 TEST_F(PrioritizedTaskRunnerTest, OrderSamePriorityByPostOrder) {
-  auto task_runner =
-      base::CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
+  auto task_runner = base::ThreadPool::CreateSequencedTaskRunner({});
   auto prioritized_task_runner =
       base::MakeRefCounted<PrioritizedTaskRunner>(task_runner);
 

net/socket/udp_socket_posix.cc

@@ -23,6 +23,7 @@
 #include "base/posix/eintr_wrapper.h"
 #include "base/rand_util.h"
 #include "base/task/post_task.h"
+#include "base/task/thread_pool.h"
 #include "base/task_runner_util.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
@@ -1328,10 +1329,8 @@ void UDPSocketPosix::FlushPending() {
 // some tests it seemed like following the advice just broke in other
 // ways.
 base::SequencedTaskRunner* UDPSocketPosix::GetTaskRunner() {
-  if (task_runner_ == nullptr) {
-    task_runner_ =
-        CreateSequencedTaskRunner(base::TaskTraits(base::ThreadPool()));
-  }
+  if (task_runner_ == nullptr)
+    task_runner_ = base::ThreadPool::CreateSequencedTaskRunner({});
   return task_runner_.get();
 }