Use an explicit PID for duplicating Pepper handles rather than the Channel's.

ipc/ipc_channel.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IPC_IPC_CHANNEL_H_
 #define IPC_IPC_CHANNEL_H_
 
 #include <string>
 
 #if defined(OS_POSIX)
@@ skipping 111 matching lines @@
   // On POSIX calling close on an IPC channel that listens for connections will
   // cause it to close any accepted connections, and it will stop listening for
   // new connections. If you just want to close the currently accepted
   // connection and listen for new ones, use ResetToAcceptingConnectionState.
   void Close();
 
   // Modify the Channel's listener.
   void set_listener(Listener* listener);
 
   // Get the process ID for the connected peer.
-  // Returns base::kNullProcessId if the peer is not connected yet.
+  //
+  // Returns base::kNullProcessId if the peer is not connected yet. Watch out
+  // for race conditions. You can easily get a channel to another process, but
+  // if your process has not yet processed the "hello" message from the remote
+  // side, this will fail. You should either make sure calling this is either
+  // in response to a message from the remote side (which guarantees that it's
+  // been connected), or you wait for the "connected" notification on the
+  // listener.
   base::ProcessId peer_pid() const;
 
   // Send a message over the Channel to the listener on the other end.
   //
   // |message| must be allocated using operator new.  This object will be
   // deleted once the contents of the Message have been sent.
   virtual bool Send(Message* message) OVERRIDE;
 
 #if defined(OS_POSIX)
   // On POSIX an IPC::Channel wraps a socketpair(), this method returns the
@@ skipping 59 matching lines @@
 
  private:
   // PIMPL to which all channel calls are delegated.
   class ChannelImpl;
   ChannelImpl *channel_impl_;
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_CHANNEL_H_