[spelling] existance to existence

media/audio/audio_system.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_AUDIO_AUDIO_SYSTEM_H_
 #define MEDIA_AUDIO_AUDIO_SYSTEM_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 25 matching lines @@
   using OnInputDeviceInfoCallback = base::OnceCallback<
       void(const AudioParameters&, const AudioParameters&, const std::string&)>;
 
   // Must not be called on audio system thread if it differs from the one
   // AudioSystem is destroyed on. See http://crbug.com/705455.
   static AudioSystem* Get();
 
   virtual ~AudioSystem();
 
   // Callback may receive invalid parameters, it means the specified device is
-  // not found. This is best-effort: valid parameters do not guarantee existance
+  // not found. This is best-effort: valid parameters do not guarantee existence
   // of the device.
   // TODO(olka,tommi): fix all AudioManager implementations to return invalid
   // parameters if the device is not found.
   virtual void GetInputStreamParameters(
       const std::string& device_id,
       OnAudioParamsCallback on_params_cb) const = 0;
 
   // If media::AudioDeviceDescription::IsDefaultDevice(device_id) is true,
   // callback will receive the parameters of the default output device.
   // Callback may receive invalid parameters, it means the specified device is
-  // not found. This is best-effort: valid parameters do not guarantee existance
+  // not found. This is best-effort: valid parameters do not guarantee existence
   // of the device.
   // TODO(olka,tommi): fix all AudioManager implementations to return invalid
   // parameters if the device is not found.
   virtual void GetOutputStreamParameters(
       const std::string& device_id,
       OnAudioParamsCallback on_params_cb) const = 0;
 
   virtual void HasInputDevices(OnBoolCallback on_has_devices_cb) const = 0;
 
   virtual void HasOutputDevices(OnBoolCallback on_has_devices_cb) const = 0;
@@ skipping 22 matching lines @@
   // Sets the global AudioSystem pointer to the specified non-null value.
   static void SetInstance(AudioSystem* audio_system);
 
   // Sets the global AudioSystem pointer to null if it equals the specified one.
   static void ClearInstance(const AudioSystem* audio_system);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_SYSTEM_H_