Make media::WallClockTimeSource thread safe.

Temporary measure until both Pipeline is reworked to provide a time
estimate to the main thread and VideoRendererImpl's internal thread
is eliminated.

This is similar to the the locking currently present in
AudioRendererImpl.

BUG=412764

Review URL: https://codereview.chromium.org/562673003

Cr-Commit-Position: refs/heads/master@{#294207}

build/sanitizers/tsan_suppressions.cc

@@ -301,9 +301,6 @@ char kTSanDefaultSuppressions[] =
 "deadlock:"
 "base::debug::TraceEventTestFixture_ThreadOnceBlocking_Test::TestBody\n"
 
-// http://crbug.com/412764
-"race:media::WallClockTimeSource::SetPlaybackRate\n"
-
 // End of suppressions.
 ;  // Please keep this semicolon.
 

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

media/base/wall_clock_time_source.h

@@ -6,6 +6,7 @@
 #define MEDIA_BASE_WALL_CLOCK_TIME_SOURCE_H_
 
 #include "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
 #include "media/base/media_export.h"
 #include "media/base/time_source.h"
 
@@ -32,6 +33,8 @@ class MEDIA_EXPORT WallClockTimeSource : public TimeSource {
   void SetTickClockForTesting(scoped_ptr<base::TickClock> tick_clock);
 
  private:
+  base::TimeDelta CurrentMediaTime_Locked();
+
   scoped_ptr<base::TickClock> tick_clock_;
   bool ticking_;
 
@@ -42,6 +45,10 @@ class MEDIA_EXPORT WallClockTimeSource : public TimeSource {
   base::TimeDelta base_time_;
   base::TimeTicks reference_wall_ticks_;
 
+  // TODO(scherkus): Remove internal locking from this class after access to
+  // Renderer::CurrentMediaTime() is single threaded http://crbug.com/370634
+  base::Lock lock_;
+
   DISALLOW_COPY_AND_ASSIGN(WallClockTimeSource);
 };