AudioManagerBase: Create and run the audio thread lazily.

media/audio/audio_low_latency_input_output_unittest.cc

Index: media/audio/audio_low_latency_input_output_unittest.cc
diff --git a/media/audio/audio_low_latency_input_output_unittest.cc b/media/audio/audio_low_latency_input_output_unittest.cc
index 9d5f5b16e305c342152a7a774a57b9e5672dec9a..010b34942099e6706e522a6d855f9e42b28f12bb 100644
--- a/media/audio/audio_low_latency_input_output_unittest.cc
+++ b/media/audio/audio_low_latency_input_output_unittest.cc
@@ -99,7 +99,7 @@ class MockAudioManager : public AudioManagerAnyPlatform {
   MockAudioManager() : AudioManagerAnyPlatform(&fake_audio_log_factory_) {}
   ~MockAudioManager() override {}
 
-  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() const override {
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() override {
     return base::MessageLoop::current()->task_runner();
   }