Revert "[base] Remove implicit-destination PostTask"

This reverts commit 50b3e1fd.

Reason for revert: crbug.com/1090992 Compile failures:

FAILED: obj/chrome/browser/browser/recovery_component_installer.o
/b/s/w/ir/cache/goma/client/gomacc ../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF...(too long)
../../chrome/browser/component_updater/recovery_component_installer.cc:419:3: error: too few arguments to function call, expected 3, have 2; did you mean 'base::ThreadPool::PostTask'?
base::PostTask(FROM_HERE, base::BindOnce(std::move(callback), result));
^~~~
base::ThreadPool::PostTask
../../base/task/thread_pool.h:95:15: note: 'base::ThreadPool::PostTask' declared here
static bool PostTask(const Location& from_here, OnceClosure task);
^

Original change's description:
> [base] Remove implicit-destination PostTask
> 
> No TaskTraits implcitly meant base::ThreadPool. The migration away
> from this paradigm is complete (task APIs v3 is bringing explicit
> API-as-destination). Remove this right away before we're ready to
> completely remove post_task.h to avoid the addition of new callers
> without an explicit destination.
> 
> Bug: 968047, 1026641
> Change-Id: I54d04872498d340cfd8ec02aa88b3e9cba1a7547
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225541
> Commit-Queue: Gabriel Charette <gab@chromium.org>
> Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#774758}

TBR=gab@chromium.org,skyostil@chromium.org

Change-Id: Ia6e764cf3293ef9ac789ce6f173951ab8e4736fe
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 968047, 1026641, 1090992
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2229410Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774796}

base/task/post_task.cc

@@ -62,6 +62,19 @@ TaskExecutor* GetTaskExecutorForTraits(const TaskTraits& traits) {
 
 }  // namespace
 
+bool PostTask(const Location& from_here, OnceClosure task) {
+  // TODO(skyostil): Make task traits required here too.
+  return PostDelayedTask(from_here, {ThreadPool()}, std::move(task),
+                         TimeDelta());
+}
+
+bool PostTaskAndReply(const Location& from_here,
+                      OnceClosure task,
+                      OnceClosure reply) {
+  return PostTaskAndReply(from_here, {ThreadPool()}, std::move(task),
+                          std::move(reply));
+}
+
 bool PostTask(const Location& from_here,
               const TaskTraits& traits,
               OnceClosure task) {

base/task/post_task.h

@@ -99,6 +99,27 @@ namespace base {
 // have to worry about this. You will encounter DCHECKs or nullptr dereferences
 // if this is violated. For tests, prefer base::test::TaskEnvironment.
 
+// Equivalent to calling PostTask with default TaskTraits.
+BASE_EXPORT bool PostTask(const Location& from_here, OnceClosure task);
+inline bool PostTask(OnceClosure task,
+                     const Location& from_here = Location::Current()) {
+  return PostTask(from_here, std::move(task));
+}
+
+// Equivalent to calling PostTaskAndReply with default TaskTraits.
+BASE_EXPORT bool PostTaskAndReply(const Location& from_here,
+                                  OnceClosure task,
+                                  OnceClosure reply);
+
+// Equivalent to calling PostTaskAndReplyWithResult with default TaskTraits.
+template <typename TaskReturnType, typename ReplyArgType>
+bool PostTaskAndReplyWithResult(const Location& from_here,
+                                OnceCallback<TaskReturnType()> task,
+                                OnceCallback<void(ReplyArgType)> reply) {
+  return PostTaskAndReplyWithResult(from_here, {ThreadPool()}, std::move(task),
+                                    std::move(reply));
+}
+
 // Posts |task| with specific |traits|. Returns false if the task definitely
 // won't run because of current shutdown state.
 BASE_EXPORT bool PostTask(const Location& from_here,

base/task/post_task_unittest.cc

@@ -99,6 +99,10 @@ class PostTaskTestWithExecutor : public ::testing::Test {
 };
 
 TEST_F(PostTaskTestWithExecutor, PostTaskToThreadPool) {
+  // Tasks without extension should not go to the TestTaskExecutor.
+  EXPECT_TRUE(PostTask(FROM_HERE, DoNothing()));
+  EXPECT_FALSE(executor_.runner()->HasPendingTask());
+
   EXPECT_TRUE(PostTask(FROM_HERE, {ThreadPool(), MayBlock()}, DoNothing()));
   EXPECT_FALSE(executor_.runner()->HasPendingTask());
 

base/threading/sequenced_task_runner_handle_unittest.cc

@@ -67,7 +67,7 @@ TEST_F(SequencedTaskRunnerHandleTest, FromThreadPoolSequencedTask) {
 }
 
 TEST_F(SequencedTaskRunnerHandleTest, NoHandleFromUnsequencedTask) {
-  base::ThreadPool::PostTask(base::BindOnce(
+  base::PostTask(base::BindOnce(
       []() { EXPECT_FALSE(SequencedTaskRunnerHandle::IsSet()); }));
   task_environment_.RunUntilIdle();
 }

content/public/test/browser_task_environment_unittest.cc

@@ -151,12 +151,12 @@ TEST(BrowserTaskEnvironmentTest, TraitsConstructor) {
   signaled_on_real_io_thread.TimedWait(base::TimeDelta::FromSeconds(5));
   EXPECT_TRUE(signaled_on_real_io_thread.IsSignaled());
 
-  // Tasks posted via ThreadPool::PostTask don't run in
-  // ThreadPoolExecutionMode::QUEUED until RunUntilIdle is called.
+  // Tasks posted via PostTask don't run in ThreadPoolExecutionMode::QUEUED
+  // until RunUntilIdle is called.
   base::AtomicFlag task_ran;
-  base::ThreadPool::PostTask(
-      FROM_HERE, BindOnce([](base::AtomicFlag* task_ran) { task_ran->Set(); },
-                          Unretained(&task_ran)));
+  PostTask(FROM_HERE,
+           BindOnce([](base::AtomicFlag* task_ran) { task_ran->Set(); },
+                    Unretained(&task_ran)));
 
   base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(100));
   EXPECT_FALSE(task_ran.IsSet());