[MessageLoop]: Replace MessageLoopCurrent::task_runner() in /components/discardable_memory.

MessageLoopCurrent::task_runner() is depecated.
This CL replaces it with with ThreadTaskRunnerHandle::Get().
A small step towards deleting MessageLoop.

This CL was generated with git cl split.
Refer to the top-level CL if necessary :
https://chromium-review.googlesource.com/c/chromium/src/+/1631693

Please CQ if LGTY!

This CL was uploaded by git cl split.

R=penghuang@chromium.org

Bug: 616447
Change-Id: I42fb5b8d372a39dfe0493d49e09caeea571bd59f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1637458
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Auto-Submit: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667190}

components/discardable_memory/service/discardable_shared_memory_manager.cc

@@ -242,9 +242,12 @@ DiscardableSharedMemoryManager::~DiscardableSharedMemoryManager() {
       this);
 
   if (mojo_thread_message_loop_) {
+    // TODO(etiennep): Get rid of mojo_thread_message_loop_ entirely.
+    DCHECK(mojo_thread_task_runner_);
     if (mojo_thread_message_loop_ == base::MessageLoopCurrent::Get()) {
       mojo_thread_message_loop_->RemoveDestructionObserver(this);
       mojo_thread_message_loop_ = base::MessageLoopCurrent::GetNull();
+      mojo_thread_task_runner_ = nullptr;
     } else {
       // If mojom::DiscardableSharedMemoryManager implementation is running in
       // another thread, we need invalidate all related weak ptrs on that
@@ -252,7 +255,7 @@ DiscardableSharedMemoryManager::~DiscardableSharedMemoryManager() {
       base::WaitableEvent event(
           base::WaitableEvent::ResetPolicy::MANUAL,
           base::WaitableEvent::InitialState::NOT_SIGNALED);
-      bool result = mojo_thread_message_loop_->task_runner()->PostTask(
+      bool result = mojo_thread_task_runner_->PostTask(
           FROM_HERE,
           base::BindOnce(
               &DiscardableSharedMemoryManager::InvalidateMojoThreadWeakPtrs,
@@ -269,9 +272,11 @@ void DiscardableSharedMemoryManager::Bind(
     const service_manager::BindSourceInfo& source_info) {
   DCHECK(!mojo_thread_message_loop_ ||
          mojo_thread_message_loop_ == base::MessageLoopCurrent::Get());
-  if (!mojo_thread_message_loop_) {
+  if (!mojo_thread_task_runner_) {
+    DCHECK(!mojo_thread_message_loop_);
     mojo_thread_message_loop_ = base::MessageLoopCurrent::Get();
     mojo_thread_message_loop_->AddDestructionObserver(this);
+    mojo_thread_task_runner_ = base::ThreadTaskRunnerHandle::Get();
   }
 
   mojo::MakeStrongBinding(
@@ -406,8 +411,7 @@ size_t DiscardableSharedMemoryManager::GetBytesAllocated() {
 void DiscardableSharedMemoryManager::WillDestroyCurrentMessageLoop() {
   // The mojo thead is going to be destroyed. We should invalidate all related
   // weak ptrs and remove the destrunction observer.
-  DCHECK(
-      mojo_thread_message_loop_->task_runner()->RunsTasksInCurrentSequence());
+  DCHECK(mojo_thread_task_runner_->RunsTasksInCurrentSequence());
   DLOG_IF(WARNING, mojo_thread_weak_ptr_factory_.HasWeakPtrs())
       << "Some MojoDiscardableSharedMemoryManagerImpls are still alive. They "
          "will be leaked.";
@@ -617,8 +621,7 @@ void DiscardableSharedMemoryManager::ScheduleEnforceMemoryPolicy() {
 
 void DiscardableSharedMemoryManager::InvalidateMojoThreadWeakPtrs(
     base::WaitableEvent* event) {
-  DCHECK(
-      mojo_thread_message_loop_->task_runner()->RunsTasksInCurrentSequence());
+  DCHECK(mojo_thread_task_runner_->RunsTasksInCurrentSequence());
   mojo_thread_weak_ptr_factory_.InvalidateWeakPtrs();
   mojo_thread_message_loop_->RemoveDestructionObserver(this);
   mojo_thread_message_loop_ = base::MessageLoopCurrent::GetNull();

components/discardable_memory/service/discardable_shared_memory_manager.h

@@ -23,6 +23,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop_current.h"
 #include "base/process/process_handle.h"
+#include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/memory_dump_provider.h"
@@ -164,6 +165,7 @@ class DISCARDABLE_MEMORY_EXPORT DiscardableSharedMemoryManager
   // A prerequisite for this is allowing objects to be bound to the lifetime
   // of a sequence directly.
   base::MessageLoopCurrent mojo_thread_message_loop_;
+  scoped_refptr<base::SingleThreadTaskRunner> mojo_thread_task_runner_;
 
   base::WeakPtrFactory<DiscardableSharedMemoryManager> weak_ptr_factory_;