Separate out IPC::Message::Sender and channel::Listener into a separate class.

ipc/ipc_channel_reader.cc

Index: ipc/ipc_channel_reader.cc
diff --git a/ipc/ipc_channel_reader.cc b/ipc/ipc_channel_reader.cc
index 5080f517c58760855d5959ecc8cac513cd4c9ff6..a8761cd0ea9c355db2a43a2d3a00be21c7e9d14b 100644
--- a/ipc/ipc_channel_reader.cc
+++ b/ipc/ipc_channel_reader.cc
@@ -7,8 +7,7 @@
 namespace IPC {
 namespace internal {
 
-ChannelReader::ChannelReader(Channel::Listener* listener)
-    : listener_(listener) {
+ChannelReader::ChannelReader(Listener* listener) : listener_(listener) {
   memset(input_buf_, 0, sizeof(input_buf_));
 }