Adding more comments to every header file in api/ subdirectory.

webrtc/api/videosourceproxy.h

Index: webrtc/api/videosourceproxy.h
diff --git a/webrtc/api/videosourceproxy.h b/webrtc/api/videosourceproxy.h
index b678acb0707929c1fd14a55f9a56dfff99569a05..a00a21d021d1491b5b5638c5762eecff42069c83 100644
--- a/webrtc/api/videosourceproxy.h
+++ b/webrtc/api/videosourceproxy.h
@@ -16,10 +16,10 @@
 
 namespace webrtc {
 
-// VideoTrackSourceInterface makes sure the real VideoTrackSourceInterface
-// implementation is
-// destroyed on the signaling thread and marshals all method calls to the
-// signaling thread.
+// Makes sure the real VideoTrackSourceInterface implementation is destroyed on
+// the signaling thread and marshals all method calls to the signaling thread.
+// TODO(deadbeef): Move this to .cc file and out of api/. What threads methods
+// are called on is an implementation detail.
 BEGIN_PROXY_MAP(VideoTrackSource)
   PROXY_SIGNALING_THREAD_DESTRUCTOR()
   PROXY_CONSTMETHOD0(SourceState, state)