Correctly handle enumerations for AudioManagers that report only the default audio output device.

content/browser/renderer_host/media/audio_output_device_enumerator.h

 // Copyright (c) 2015 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.
 
 // AudioOutputDeviceEnumerator is used to enumerate audio output devices.
 // It can return cached results of previous enumerations in order to boost
 // performance.
 // All its public methods must be called on the thread where the object is
 // created.
 
@@ skipping 25 matching lines @@
 
 // AudioOutputDeviceInfo describes information about an audio output device.
 // The enumerations returned by AudioOutputDeviceEnumerator::Enumerate() contain
 // elements of this type. It is used only in the browser side.
 struct AudioOutputDeviceInfo {
   std::string unique_id;
   std::string device_name;
   media::AudioParameters output_params;
 };
 
-typedef std::vector<AudioOutputDeviceInfo> AudioOutputDeviceEnumeration;
+// The result of an enumeration. It is used only in the browser side.
+struct AudioOutputDeviceEnumeration {
+ public:
+  AudioOutputDeviceEnumeration(
+      const std::vector<AudioOutputDeviceInfo>& devices,
+      bool has_actual_devices);
+  AudioOutputDeviceEnumeration();
+  ~AudioOutputDeviceEnumeration();
+
+  std::vector<AudioOutputDeviceInfo> devices;
+  bool has_actual_devices;
+};
+
 typedef base::Callback<void(const AudioOutputDeviceEnumeration&)>
     AudioOutputDeviceEnumerationCB;
 
 class CONTENT_EXPORT AudioOutputDeviceEnumerator {
  public:
   enum CachePolicy {
     CACHE_POLICY_NO_CACHING,
     CACHE_POLICY_MANUAL_INVALIDATION
   };
   AudioOutputDeviceEnumerator(media::AudioManager* audio_manager,
                               CachePolicy cache_policy);
   ~AudioOutputDeviceEnumerator();
 
   // Does an enumeration and provides the results to the callback.
   // If there are no physical devices, the result contains a single entry with
-  // the default parameters provided by the underlying audio manager.
+  // the default parameters provided by the underlying audio manager and with
+  // the |has_actual_devices| field set to false.
   // The behavior with no physical devices is there to ease the transition
   // from the use of RenderThreadImpl::GetAudioHardwareConfig(), which always
   // provides default parameters, even if there are no devices.
   // See https://crbug.com/549125.
+  // Some audio managers always report a single device, regardless of the
+  // physical devices in the system. In this case the |has_actual_devices| field
+  // is set to true to differentiate from the case of no physical devices.
   void Enumerate(const AudioOutputDeviceEnumerationCB& callback);
 
   // Invalidates the current cache.
   void InvalidateCache();
 
   // Sets the cache policy.
   void SetCachePolicy(CachePolicy cache_policy);
 
   // Returns true if the caching policy is different from
   // CACHE_POLICY_NO_CACHING, false otherwise.
@@ skipping 21 matching lines @@
 
   base::ThreadChecker thread_checker_;
   base::WeakPtrFactory<AudioOutputDeviceEnumerator> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputDeviceEnumerator);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_OUTPUT_DEVICE_ENUMERATOR_H_