Protect mock time variables in TestMockTimeTaskRunner by a lock

|now_| and |now_ticks_| in TestMockTimeTaskRunner were read or written
without a lock. So, when PostDelayedTask() and NowTicks() are called
on different threads, it hits TSan failure.

This CL adds lock for all access to them to avoid the data race.

Change-Id: I562e2bfbd46b481b41faa05906b19c8664654812
Reviewed-on: https://chromium-review.googlesource.com/798819Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520779}

base/test/test_mock_time_task_runner.cc

@@ -209,7 +209,7 @@ void TestMockTimeTaskRunner::FastForwardBy(TimeDelta delta) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_GE(delta, TimeDelta());
 
-  const TimeTicks original_now_ticks = now_ticks_;
+  const TimeTicks original_now_ticks = NowTicks();
   ProcessAllTasksNoLaterThan(delta);
   ForwardClocksUntilTickTime(original_now_ticks + delta);
 }
@@ -232,12 +232,12 @@ void TestMockTimeTaskRunner::ClearPendingTasks() {
 }
 
 Time TestMockTimeTaskRunner::Now() const {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  AutoLock scoped_lock(tasks_lock_);
   return now_;
 }
 
 TimeTicks TestMockTimeTaskRunner::NowTicks() const {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  AutoLock scoped_lock(tasks_lock_);
   return now_ticks_;
 }
 
@@ -278,7 +278,7 @@ size_t TestMockTimeTaskRunner::GetPendingTaskCount() const {
 TimeDelta TestMockTimeTaskRunner::NextPendingTaskDelay() const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return tasks_.empty() ? TimeDelta::Max()
-                        : tasks_.top().GetTimeToRun() - now_ticks_;
+                        : tasks_.top().GetTimeToRun() - NowTicks();
 }
 
 // TODO(gab): Combine |thread_checker_| with a SequenceToken to differentiate
@@ -330,7 +330,7 @@ void TestMockTimeTaskRunner::ProcessAllTasksNoLaterThan(TimeDelta max_delta) {
     undo_override = ThreadTaskRunnerHandle::OverrideForTesting(this);
   }
 
-  const TimeTicks original_now_ticks = now_ticks_;
+  const TimeTicks original_now_ticks = NowTicks();
   while (!quit_run_loop_) {
     OnBeforeSelectingTask();
     TestPendingTask task_info;
@@ -347,11 +347,14 @@ void TestMockTimeTaskRunner::ProcessAllTasksNoLaterThan(TimeDelta max_delta) {
 
 void TestMockTimeTaskRunner::ForwardClocksUntilTickTime(TimeTicks later_ticks) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  if (later_ticks <= now_ticks_)
-    return;
+  {
+    AutoLock scoped_lock(tasks_lock_);
+    if (later_ticks <= now_ticks_)
+      return;
 
-  now_ += later_ticks - now_ticks_;
-  now_ticks_ = later_ticks;
+    now_ += later_ticks - now_ticks_;
+    now_ticks_ = later_ticks;
+  }
   OnAfterTimePassed();
 }
 

base/test/test_mock_time_task_runner.h

@@ -246,7 +246,7 @@ class TestMockTimeTaskRunner : public SingleThreadTaskRunner,
   // |tasks_lock_| is held.
   size_t next_task_ordinal_ = 0;
 
-  Lock tasks_lock_;
+  mutable Lock tasks_lock_;
   ConditionVariable tasks_lock_cv_;
 
   // Members used to in TestMockTimeTaskRunners of Type::kBoundToThread to take