Add publicly visible mocks for AudioSourceInterface and AudioTrackInterface

Bug: webrtc:11642
Change-Id: Ia8807623ea7ca2e49fc795b907aec83fd10e3305
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/191821
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32563}
diff --git a/api/BUILD.gn b/api/BUILD.gn
index fd27681..e0c7934 100644
--- a/api/BUILD.gn
+++ b/api/BUILD.gn
@@ -865,6 +865,17 @@
     ]
   }
 
+  rtc_source_set("mock_media_stream_interface") {
+    visibility = [ "*" ]
+    testonly = true
+    sources = [ "test/mock_media_stream_interface.h" ]
+
+    deps = [
+      ":media_stream_interface",
+      "../test:test_support",
+    ]
+  }
+
   rtc_source_set("dummy_peer_connection") {
     visibility = [ "*" ]
     testonly = true
@@ -1051,6 +1062,7 @@
       ":mock_data_channel",
       ":mock_frame_decryptor",
       ":mock_frame_encryptor",
+      ":mock_media_stream_interface",
       ":mock_peer_connection_factory_interface",
       ":mock_peerconnectioninterface",
       ":mock_rtp",