ipc: Create an unforgeable mechanism to get the process id of the sender.

ipc/ipc_channel_reader.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_READER_H_
 #define IPC_IPC_CHANNEL_READER_H_
 
 #include <set>
 
 #include "base/basictypes.h"
@@ skipping 96 matching lines @@
 
   // Handles internal messages, like the hello message sent on channel startup.
   virtual void HandleInternalMessage(const Message& msg) = 0;
 
   // Exposed for testing purposes only.
   ScopedVector<Message>* get_queued_messages() { return &queued_messages_; }
 
   // Exposed for testing purposes only.
   virtual void DispatchMessage(Message* m);
 
+  // Get the process ID for the sender of the message.
+  virtual base::ProcessId GetSenderPID() = 0;
+
  private:
   FRIEND_TEST_ALL_PREFIXES(ChannelReaderTest, AttachmentAlreadyBrokered);
   FRIEND_TEST_ALL_PREFIXES(ChannelReaderTest, AttachmentNotYetBrokered);
 
   typedef std::set<BrokerableAttachment::AttachmentId> AttachmentIdSet;
 
   // Takes the given data received from the IPC channel, translates it into
   // Messages, and puts them in queued_messages_.
   // As an optimization, after a message is translated, the message is
   // immediately dispatched if able. This prevents an otherwise unnecessary deep
@@ skipping 38 matching lines @@
   // set contains the AttachmentIds that are needed to unblock the message.
   AttachmentIdSet blocked_ids_;
 
   DISALLOW_COPY_AND_ASSIGN(ChannelReader);
 };
 
 }  // namespace internal
 }  // namespace IPC
 
 #endif  // IPC_IPC_CHANNEL_READER_H_