Move IPC::MessageFilter and router to a separate file

content/child/child_message_filter.h

Index: content/child/child_message_filter.h
diff --git a/content/child/child_message_filter.h b/content/child/child_message_filter.h
index 21cccac065a9a81b3f3f7c4e36ca70b6eda6b8a0..0d9c4ffc41cba47db9a267e131915455d3f6ecfa 100644
--- a/content/child/child_message_filter.h
+++ b/content/child/child_message_filter.h
@@ -5,12 +5,17 @@
 #ifndef CONTENT_CHILD_CROSS_MESSAGE_FILTER_H_
 #define CONTENT_CHILD_CROSS_MESSAGE_FILTER_H_
 
-#include "ipc/ipc_channel_proxy.h"
+#include "base/memory/ref_counted.h"
+#include "ipc/ipc_sender.h"
 
 namespace base {
 class TaskRunner;
 }
 
+namespace IPC {
+class MessageFilter;
+}
+
 namespace content {
 
 class ThreadSafeSender;
@@ -52,10 +57,10 @@ class ChildMessageFilter
 
   friend class base::RefCountedThreadSafe<ChildMessageFilter>;
 
-  IPC::ChannelProxy::MessageFilter* GetFilter();
+  IPC::MessageFilter* GetFilter();
 
-  // This implements IPC::ChannelProxy::MessageFilter to hide the actual
-  // filter methods from child classes.
+  // This implements IPC::MessageFilter to hide the actual filter methods from
+  // child classes.
   Internal* internal_;
 
   scoped_refptr<ThreadSafeSender> thread_safe_sender_;