Getting rid of AudioHardwareConfig and its synchronous IPC.

content/renderer/media/audio_renderer_sink_cache_impl.h

Index: content/renderer/media/audio_renderer_sink_cache_impl.h
diff --git a/content/renderer/media/audio_renderer_sink_cache_impl.h b/content/renderer/media/audio_renderer_sink_cache_impl.h
index 7d163d9074c606acae482c5f181f2ecc732cf7ce..f0f5867c1ade50509c84690d9261ba1f7521d4ff 100644
--- a/content/renderer/media/audio_renderer_sink_cache_impl.h
+++ b/content/renderer/media/audio_renderer_sink_cache_impl.h
@@ -9,6 +9,7 @@
 
 #include <vector>
 
+#include "base/optional.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
@@ -91,6 +92,12 @@ class CONTENT_EXPORT AudioRendererSinkCacheImpl
   base::Lock cache_lock_;
   CacheContainer cache_;
 
+  // Cached default output device information. Since access to the default
+  // device is always allowed, this information can be cashed and shared among
+  // all the clients. It is updated on the first request if not initialized yet,
+  // and each time a new default device sink is created in the cache.
+  base::Optional<media::OutputDeviceInfo> default_device_info_;
+
   // Weak pointer to be used for delayed sink deletion on |task_runner_|.
   // Pre-created in constructor and is used to post all the delayed tasks.
   // A delayed task can be concurrently posted from any thread the cache is used