Make media::WallClockTimeSource thread safe.

media/base/wall_clock_time_source.cc

Index: media/base/wall_clock_time_source.cc
diff --git a/media/base/wall_clock_time_source.cc b/media/base/wall_clock_time_source.cc
index f7a8f6ef894d843ba9dd67dc46013ffbc822ce2d..5d826435576421913ab48ed8b313644420245721 100644
--- a/media/base/wall_clock_time_source.cc
+++ b/media/base/wall_clock_time_source.cc
@@ -19,23 +19,26 @@ WallClockTimeSource::~WallClockTimeSource() {
 }
 
 void WallClockTimeSource::StartTicking() {
+  base::AutoLock auto_lock(lock_);
   DCHECK(!ticking_);
   ticking_ = true;
   reference_wall_ticks_ = tick_clock_->NowTicks();
 }
 
 void WallClockTimeSource::StopTicking() {
+  base::AutoLock auto_lock(lock_);
   DCHECK(ticking_);
-  base_time_ = CurrentMediaTime();
+  base_time_ = CurrentMediaTime_Locked();
   ticking_ = false;
   reference_wall_ticks_ = tick_clock_->NowTicks();
 }
 
 void WallClockTimeSource::SetPlaybackRate(float playback_rate) {
+  base::AutoLock auto_lock(lock_);
   // Estimate current media time using old rate to use as a new base time for
   // the new rate.
   if (ticking_) {
-    base_time_ = CurrentMediaTime();
+    base_time_ = CurrentMediaTime_Locked();
     reference_wall_ticks_ = tick_clock_->NowTicks();
   }
 
@@ -43,18 +46,14 @@ void WallClockTimeSource::SetPlaybackRate(float playback_rate) {
 }
 
 void WallClockTimeSource::SetMediaTime(base::TimeDelta time) {
+  base::AutoLock auto_lock(lock_);
   CHECK(!ticking_);
   base_time_ = time;
 }
 
 base::TimeDelta WallClockTimeSource::CurrentMediaTime() {
-  if (!ticking_)
-    return base_time_;
-
-  base::TimeTicks now = tick_clock_->NowTicks();
-  return base_time_ +
-         base::TimeDelta::FromMicroseconds(
-             (now - reference_wall_ticks_).InMicroseconds() * playback_rate_);
+  base::AutoLock auto_lock(lock_);
+  return CurrentMediaTime_Locked();
 }
 
 base::TimeDelta WallClockTimeSource::CurrentMediaTimeForSyncingVideo() {
@@ -66,4 +65,15 @@ void WallClockTimeSource::SetTickClockForTesting(
   tick_clock_.swap(tick_clock);
 }
 
+base::TimeDelta WallClockTimeSource::CurrentMediaTime_Locked() {
+  lock_.AssertAcquired();
+  if (!ticking_)
+    return base_time_;
+
+  base::TimeTicks now = tick_clock_->NowTicks();
+  return base_time_ +
+         base::TimeDelta::FromMicroseconds(
+             (now - reference_wall_ticks_).InMicroseconds() * playback_rate_);
+}
+
 }  // namespace media