Remove IPC_BEGIN_MESSAGE_MAP_EX macro since r270839 made all bad IPCs kill their child processes.

chrome/browser/signin/principals_message_filter.h

Index: chrome/browser/signin/principals_message_filter.h
===================================================================
--- chrome/browser/signin/principals_message_filter.h	(revision 271040)
+++ chrome/browser/signin/principals_message_filter.h	(working copy)
@@ -20,8 +20,7 @@
   virtual void OverrideThreadForMessage(
       const IPC::Message& message,
       content::BrowserThread::ID* thread) OVERRIDE;
-  virtual bool OnMessageReceived(const IPC::Message& message,
-                                 bool* message_was_ok) OVERRIDE;
+  virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
  private:
   virtual ~PrincipalsMessageFilter();