Revert of Add lock to fix race in AudioRendererMixerInput.

media/base/audio_renderer_mixer_input.cc

Index: media/base/audio_renderer_mixer_input.cc
diff --git a/media/base/audio_renderer_mixer_input.cc b/media/base/audio_renderer_mixer_input.cc
index f9905383c4cba1f9b9108a8d330e4be10040df9c..5743700f04b0a62c1c3c6eaf0f2d0bfa54aef0f5 100644
--- a/media/base/audio_renderer_mixer_input.cc
+++ b/media/base/audio_renderer_mixer_input.cc
@@ -29,22 +29,15 @@
       mixer_(nullptr),
       callback_(nullptr),
       error_cb_(base::Bind(&AudioRendererMixerInput::OnRenderError,
-                           base::Unretained(this))) {
-  // Can be constructed on any thread, but sink operations should all occur
-  // on same thread.
-  thread_checker_.DetachFromThread();
-}
+                           base::Unretained(this))) {}
 
 AudioRendererMixerInput::~AudioRendererMixerInput() {
-  DCHECK(!started_);
   DCHECK(!mixer_);
 }
 
 void AudioRendererMixerInput::Initialize(
     const AudioParameters& params,
     AudioRendererSink::RenderCallback* callback) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(!started_);
   DCHECK(!mixer_);
   DCHECK(callback);
 
@@ -53,7 +46,6 @@
 }
 
 void AudioRendererMixerInput::Start() {
-  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!started_);
   DCHECK(!mixer_);
   DCHECK(callback_);  // Initialized.
@@ -76,8 +68,6 @@
 }
 
 void AudioRendererMixerInput::Stop() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   // Stop() may be called at any time, if Pause() hasn't been called we need to
   // remove our mixer input before shutdown.
   Pause();
@@ -100,8 +90,6 @@
 }
 
 void AudioRendererMixerInput::Play() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   if (playing_ || !mixer_)
     return;
 
@@ -110,8 +98,6 @@
 }
 
 void AudioRendererMixerInput::Pause() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   if (!playing_ || !mixer_)
     return;
 
@@ -120,8 +106,6 @@
 }
 
 bool AudioRendererMixerInput::SetVolume(double volume) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  base::AutoLock auto_lock(volume_lock_);
   volume_ = volume;
   return true;
 }
@@ -134,8 +118,6 @@
     const std::string& device_id,
     const url::Origin& security_origin,
     const SwitchOutputDeviceCB& callback) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   if (!mixer_) {
     if (pending_switch_callback_.is_null()) {
       pending_switch_callback_ = callback;
@@ -177,16 +159,12 @@
 }
 
 AudioParameters AudioRendererMixerInput::GetOutputParameters() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   if (mixer_)
     return mixer_->GetOutputDevice()->GetOutputParameters();
   return get_hardware_params_cb_.Run(device_id_, security_origin_);
 }
 
 OutputDeviceStatus AudioRendererMixerInput::GetDeviceStatus() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   if (mixer_)
     return mixer_->GetOutputDevice()->GetDeviceStatus();
 
@@ -198,11 +176,6 @@
 
 double AudioRendererMixerInput::ProvideInput(AudioBus* audio_bus,
                                              base::TimeDelta buffer_delay) {
-  // No thread checker here. This method is called on a different thread as part
-  // of audio rendering. AudioRendererMixer has locks that protect us from
-  // things like attempting to ProvideInput while simultaneously removing
-  // ourselves from mixer inputs (see Pause()).
-
   // TODO(chcunningham): Delete this conversion and change ProvideInput to more
   // precisely describe delay as a count of frames delayed instead of TimeDelta.
   // See http://crbug.com/587522.
@@ -217,11 +190,7 @@
         frames_filled, audio_bus->frames() - frames_filled);
   }
 
-  // Synchronize access to |volume_| with SetVolume().
-  {
-    base::AutoLock auto_lock(volume_lock_);
-    return frames_filled > 0 ? volume_ : 0;
-  }
+  return frames_filled > 0 ? volume_ : 0;
 }
 
 void AudioRendererMixerInput::OnRenderError() {