Added an empty AudioTransportProxy to AudioState.

webrtc/audio/BUILD.gn

Index: webrtc/audio/BUILD.gn
diff --git a/webrtc/audio/BUILD.gn b/webrtc/audio/BUILD.gn
index 127900544cb55dfa9b4ed414e5f884d378b7856d..abdc96806d252cf05b33a116bade28a6409532a0 100644
--- a/webrtc/audio/BUILD.gn
+++ b/webrtc/audio/BUILD.gn
@@ -16,6 +16,7 @@ rtc_static_library("audio") {
     "audio_send_stream.h",
     "audio_state.cc",
     "audio_state.h",
+    "audio_transport_proxy.h",
     "conversion.h",
     "scoped_voe_interface.h",
   ]
@@ -29,6 +30,9 @@ rtc_static_library("audio") {
     "..:webrtc_common",
     "../api:audio_mixer_api",
     "../api:call_api",
+    "../base:rtc_base_approved",
+    "../modules/audio_device",
+    "../modules/audio_processing",
     "../system_wrappers",
     "../voice_engine",
   ]
@@ -50,5 +54,13 @@ if (rtc_include_tests) {
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
       suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
     }
+    if (is_win) {

[the sun, 2016/11/09 09:41:52]

Where do you get this warning? Is there any way we can work around it without
adding clutter to the build configs?

[aleloi, 2016/11/09 16:37:00]

I don't think so, but I'll investigate: the code that results in the warning
originates somewhere in gmock. I've commented this out in the meantime to look
at the compilation error once again.

What we probably could (and should) do is to create a target for the mock
dependency and move the flag to it.

[aleloi, 2016/11/10 16:44:39]

Solved in https://codereview.webrtc.org/2492713003 ! I added a target
|audio_device:mock_audio_device| for the mock dependency and a config
|audio_device:mock_audio_device_config| in that target that is applied to
everything that depends on the mock audio device.

+      cflags = [
+        # TODO(phoglund): get rid of 4373 supression when
+        # http://code.google.com/p/webrtc/issues/detail?id=261 is solved.
+        # legacy warning for ignoring const / volatile in signatures.
+        "/wd4373",
+      ]
+    }
   }
 }