Add AudioStreamRegistry. Move stream counting logic

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 9431458c119e8afecf1f285dfa0816bbafe29024..53394bfeaf38d0fa2b5b0a067215afeb708c74ba 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -141,6 +141,8 @@ static_library("test_support") {
     "fake_compositor_dependencies.h",
     "fake_plugin_service.cc",
     "fake_plugin_service.h",
+    "mock_audio_stream_registry.cc",
+    "mock_audio_stream_registry.h",
     "mock_background_sync_controller.cc",
     "mock_background_sync_controller.h",
     "mock_google_streaming_server.cc",
@@ -1188,6 +1190,7 @@ test("content_unittests") {
     "../browser/renderer_host/media/audio_output_authorization_handler_unittest.cc",
     "../browser/renderer_host/media/audio_output_delegate_unittest.cc",
     "../browser/renderer_host/media/audio_renderer_host_unittest.cc",
+    "../browser/renderer_host/media/audio_stream_registry_impl_unittest.cc",
     "../browser/renderer_host/media/media_devices_dispatcher_host_unittest.cc",
     "../browser/renderer_host/media/media_devices_manager_unittest.cc",
     "../browser/renderer_host/media/media_stream_dispatcher_host_unittest.cc",