Make dependency of audio_device of ApplicationServices explicit.
Tested in https://codereview.webrtc.org/2276903002.

BUG=webrtc:6170
NOTRY=true

Review-Url: https://codereview.webrtc.org/2273713003
Cr-Commit-Position: refs/heads/master@{#13895}
diff --git a/webrtc/modules/audio_device/BUILD.gn b/webrtc/modules/audio_device/BUILD.gn
index 6514946..3f74ff6 100644
--- a/webrtc/modules/audio_device/BUILD.gn
+++ b/webrtc/modules/audio_device/BUILD.gn
@@ -137,6 +137,9 @@
           "mac/portaudio/pa_ringbuffer.h",
         ]
         libs = [
+          # Needed for CoreGraphics:
+          "ApplicationServices.framework",
+
           "AudioToolbox.framework",
           "CoreAudio.framework",