[scheduler]: Add Add/RemoveTaskObserver to NestableSingleThreadTaskRunner interface.

Adds the Add/RemoveTaskObserver functions to the NestableSingleThreadTaskRunner
interface such that they can be implemented by the SchedulerMessageLoopDelegate
and mocked out for the NestableTaskRunnerForTest. This avoids calling
base::MessageLoop::current() in task queue manager.

BUG=485371

Review URL: https://codereview.chromium.org/1160083003

Cr-Commit-Position: refs/heads/master@{#331978}

6 files changed, 35 insertions, 2 deletions

diff --git a/components/scheduler/child/nestable_single_thread_task_runner.h b/components/scheduler/child/nestable_single_thread_task_runner.h
index e1bf990..0b507a2 100644
--- a/components/scheduler/child/nestable_single_thread_task_runner.h
+++ b/components/scheduler/child/nestable_single_thread_task_runner.h
@@ -6,6 +6,7 @@
 #define COMPONENTS_SCHEDULER_CHILD_NESTABLE_SINGLE_THREAD_TASK_RUNNER_H_
 
 #include "base/single_thread_task_runner.h"
+#include "base/message_loop/message_loop.h"
 #include "components/scheduler/scheduler_export.h"
 
 namespace scheduler {
@@ -20,6 +21,12 @@ class SCHEDULER_EXPORT NestableSingleThreadTaskRunner
   // a nested task).
   virtual bool IsNested() const = 0;
 
+  // Adds and removes MessageLoop::TaskObservers to the task runner.
+  virtual void AddTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) = 0;
+  virtual void RemoveTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) = 0;
+
  protected:
   ~NestableSingleThreadTaskRunner() override {}
 
diff --git a/components/scheduler/child/nestable_task_runner_for_test.cc b/components/scheduler/child/nestable_task_runner_for_test.cc
index 42e1264..8a7a341 100644
--- a/components/scheduler/child/nestable_task_runner_for_test.cc
+++ b/components/scheduler/child/nestable_task_runner_for_test.cc
@@ -46,4 +46,12 @@ void NestableTaskRunnerForTest::SetNested(bool is_nested) {
   is_nested_ = is_nested;
 }
 
+void NestableTaskRunnerForTest::AddTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+}
+
+void NestableTaskRunnerForTest::RemoveTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+}
+
 }  // namespace scheduler
diff --git a/components/scheduler/child/nestable_task_runner_for_test.h b/components/scheduler/child/nestable_task_runner_for_test.h
index 6905620..5ef4eec 100644
--- a/components/scheduler/child/nestable_task_runner_for_test.h
+++ b/components/scheduler/child/nestable_task_runner_for_test.h
@@ -25,6 +25,10 @@ class NestableTaskRunnerForTest : public NestableSingleThreadTaskRunner {
                                   base::TimeDelta delay) override;
   bool RunsTasksOnCurrentThread() const override;
   bool IsNested() const override;
+  void AddTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) override;
+  void RemoveTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) override;
 
  protected:
   ~NestableTaskRunnerForTest() override;
diff --git a/components/scheduler/child/scheduler_message_loop_delegate.cc b/components/scheduler/child/scheduler_message_loop_delegate.cc
index 8c06e30..ba0d6b4 100644
--- a/components/scheduler/child/scheduler_message_loop_delegate.cc
+++ b/components/scheduler/child/scheduler_message_loop_delegate.cc
@@ -43,4 +43,14 @@ bool SchedulerMessageLoopDelegate::IsNested() const {
   return message_loop_->IsNested();
 }
 
+void SchedulerMessageLoopDelegate::AddTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+  return message_loop_->AddTaskObserver(task_observer);
+}
+
+void SchedulerMessageLoopDelegate::RemoveTaskObserver(
+    base::MessageLoop::TaskObserver* task_observer) {
+  return message_loop_->RemoveTaskObserver(task_observer);
+}
+
 }  // namespace scheduler
diff --git a/components/scheduler/child/scheduler_message_loop_delegate.h b/components/scheduler/child/scheduler_message_loop_delegate.h
index 2fce4b6..ce2ad48 100644
--- a/components/scheduler/child/scheduler_message_loop_delegate.h
+++ b/components/scheduler/child/scheduler_message_loop_delegate.h
@@ -27,6 +27,10 @@ class SCHEDULER_EXPORT SchedulerMessageLoopDelegate
                                   base::TimeDelta delay) override;
   bool RunsTasksOnCurrentThread() const override;
   bool IsNested() const override;
+  void AddTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) override;
+  void RemoveTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) override;
 
  protected:
   ~SchedulerMessageLoopDelegate() override;
diff --git a/components/scheduler/child/task_queue_manager.cc b/components/scheduler/child/task_queue_manager.cc
index 366c682..d9fa47c 100644
--- a/components/scheduler/child/task_queue_manager.cc
+++ b/components/scheduler/child/task_queue_manager.cc
@@ -712,14 +712,14 @@ void TaskQueueManager::SetWorkBatchSize(int work_batch_size) {
 void TaskQueueManager::AddTaskObserver(
     base::MessageLoop::TaskObserver* task_observer) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
-  base::MessageLoop::current()->AddTaskObserver(task_observer);
+  main_task_runner_->AddTaskObserver(task_observer);
   task_observers_.AddObserver(task_observer);
 }
 
 void TaskQueueManager::RemoveTaskObserver(
     base::MessageLoop::TaskObserver* task_observer) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
-  base::MessageLoop::current()->RemoveTaskObserver(task_observer);
+  main_task_runner_->RemoveTaskObserver(task_observer);
   task_observers_.RemoveObserver(task_observer);
 }