Make IPC channels track their peer process ID

ipc/ipc_channel_win.h

Index: ipc/ipc_channel_win.h
===================================================================
--- ipc/ipc_channel_win.h	(revision 130443)
+++ ipc/ipc_channel_win.h	(working copy)
@@ -33,6 +33,7 @@
   void Close();
   bool Send(Message* message);
   static bool IsNamedServerInitialized(const std::string& channel_id);
+  base::ProcessId peer_pid() const { return peer_pid_; }
 
  private:
   // ChannelReader implementation.
@@ -67,6 +68,8 @@
 
   HANDLE pipe_;
 
+  base::ProcessId peer_pid_;
+
   // Messages to be sent are queued here.
   std::queue<Message*> output_queue_;