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 1fd0646b30693e31918b5c69f44f8063c2089928..de4b09fca6a42f2313457a010a374cca45df9eaf 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -143,6 +143,8 @@ 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",
@@ -1196,6 +1198,7 @@ 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",