Move more sources from modules.gypi to subdirectories.

third_party/WebKit/Source/modules/audio_output_devices/BUILD.gn

Index: third_party/WebKit/Source/modules/audio_output_devices/BUILD.gn
diff --git a/third_party/WebKit/Source/modules/audio_output_devices/BUILD.gn b/third_party/WebKit/Source/modules/audio_output_devices/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..7289bf8f19681b9c9ecb3b53535573fb7b6b155a
--- /dev/null
+++ b/third_party/WebKit/Source/modules/audio_output_devices/BUILD.gn
@@ -0,0 +1,16 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//third_party/WebKit/Source/modules/modules.gni")
+
+blink_modules_sources("audio_output_devices") {
+  sources = [
+    "AudioOutputDeviceClient.cpp",
+    "AudioOutputDeviceClient.h",
+    "HTMLMediaElementAudioOutputDevice.cpp",
+    "HTMLMediaElementAudioOutputDevice.h",
+    "SetSinkIdCallbacks.cpp",
+    "SetSinkIdCallbacks.h",
+  ]
+}