Add AudioManager::GetAudioOutputDeviceNames and implement for pulseaudio.

media/media.gyp

Index: media/media.gyp
diff --git a/media/media.gyp b/media/media.gyp
index ab2701881dd76e422e62f20d981e9d6cf9265145..7eb45543eb76b5fad89f62c36fbaf582610efb08 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -913,6 +913,7 @@
         'audio/audio_input_unittest.cc',
         'audio/audio_input_volume_unittest.cc',
         'audio/audio_low_latency_input_output_unittest.cc',
+        'audio/audio_manager_unittest.cc',
         'audio/audio_output_controller_unittest.cc',
         'audio/audio_output_device_unittest.cc',
         'audio/audio_output_proxy_unittest.cc',
@@ -1038,6 +1039,11 @@
             'base/media_file_checker_unittest.cc',
           ],
         }],
+        ['use_pulseaudio==1', {
+          'defines': [
+            'USE_PULSEAUDIO',
+          ],
+        }],
         ['os_posix==1 and OS!="mac" and OS!="ios"', {
           'conditions': [
             ['linux_use_tcmalloc==1', {