Make IPC channels track their peer process ID

ipc/ipc_channel_posix.h

Index: ipc/ipc_channel_posix.h
===================================================================
--- ipc/ipc_channel_posix.h	(revision 130443)
+++ ipc/ipc_channel_posix.h	(working copy)
@@ -15,6 +15,7 @@
 #include <vector>
 
 #include "base/message_loop.h"
+#include "base/process.h"
 #include "ipc/file_descriptor_set_posix.h"
 #include "ipc/ipc_channel_reader.h"
 
@@ -65,6 +66,7 @@
   bool HasAcceptedConnection() const;
   bool GetClientEuid(uid_t* client_euid) const;
   void ResetToAcceptingConnectionState();
+  base::ProcessId peer_pid() const { return peer_pid_; }
   static bool IsNamedServerInitialized(const std::string& channel_id);
 #if defined(OS_LINUX)
   static void SetGlobalPid(int pid);
@@ -113,6 +115,8 @@
 
   Mode mode_;
 
+  base::ProcessId peer_pid_;
+
   // After accepting one client connection on our server socket we want to
   // stop listening.
   MessageLoopForIO::FileDescriptorWatcher server_listen_connection_watcher_;