Move IPC::MessageFilter and router to a separate file

content/child/db_message_filter.h

Index: content/child/db_message_filter.h
diff --git a/content/child/db_message_filter.h b/content/child/db_message_filter.h
index 4950006f4da851a96723c8e7077a8ca73833b45b..7297a04817d782ed74d7abe67ee1c0aed21d32e1 100644
--- a/content/child/db_message_filter.h
+++ b/content/child/db_message_filter.h
@@ -5,17 +5,18 @@
 #ifndef CONTENT_CHILD_DB_MESSAGE_FILTER_H_
 #define CONTENT_CHILD_DB_MESSAGE_FILTER_H_
 
-#include "ipc/ipc_channel_proxy.h"
+#include "base/strings/string16.h"
+#include "ipc/message_filter.h"
 
 namespace content {
 
 // Receives database messages from the browser process and processes them on the
 // IO thread.
-class DBMessageFilter : public IPC::ChannelProxy::MessageFilter {
+class DBMessageFilter : public IPC::MessageFilter {
  public:
   DBMessageFilter();
 
-  // IPC::ChannelProxy::MessageFilter
+  // IPC::MessageFilter
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
  protected: