Move AudioDecoder and related stuff to the api/ directory

webrtc/api/DEPS

Index: webrtc/api/DEPS
diff --git a/webrtc/api/DEPS b/webrtc/api/DEPS
index 4543a44d751936ac56990e0963eae51f7d1cacca..0b3778bde22a8204659458ced5130cec5680fffb 100644
--- a/webrtc/api/DEPS
+++ b/webrtc/api/DEPS
@@ -12,9 +12,11 @@ specific_include_rules = {
     "+webrtc/voice_engine",
   ],
 
-  # TODO(kwiberg): Remove this exception when audio_decoder_factory.h
-  # has moved to api/.
-  "peerconnectioninterface\.h": [
-    "+webrtc/modules/audio_coding/codecs/audio_decoder_factory.h",
+  # We allow .cc files in webrtc/api/ to #include a bunch of stuff
+  # that's off-limits for the .h files. That's because .h files leak
+  # their #includes to whoever's #including them, but .cc files do not
+  # since no one #includes them.
+  ".*\.cc": [
+    "+webrtc/modules/audio_coding",
   ],
 }