Create new class "CastTransport", which encapsulates the message read and write event loops.

extensions/browser/api/cast_channel/cast_socket.h

Index: extensions/browser/api/cast_channel/cast_socket.h
diff --git a/extensions/browser/api/cast_channel/cast_socket.h b/extensions/browser/api/cast_channel/cast_socket.h
index bd1e377d3f8ada42ffb136dfc755aec7c6d7a054..a5ea48910ff3666f282e753808d7c052fa57287f 100644
--- a/extensions/browser/api/cast_channel/cast_socket.h
+++ b/extensions/browser/api/cast_channel/cast_socket.h
@@ -47,11 +47,12 @@ class MessageFramer;
 //
 // NOTE: Not called "CastChannel" to reduce confusion with the generated API
 // code.
+// TODO(kmarshall): Inherit from CastSocket and rename to CastSocketImpl.
 class CastSocket : public ApiResource {
  public:
-  // Object to be informed of incoming messages and errors.  The CastSocket that
-  // owns the delegate must not be deleted by it, only by the ApiResourceManager
-  // or in the callback to Close().
+  // Object to be informed of incoming messages and errors.  The CastSocket
+  // that owns the delegate must not be deleted by it, only by the
+  // ApiResourceManager or in the callback to Close().
   class Delegate {
    public:
     // An error occurred on the channel. |last_errors| contains the last errors