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

ipc/ipc_message.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_MESSAGE_H_
 #define IPC_IPC_MESSAGE_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 166 matching lines @@
   // writes it to |*attachment|. It returns true on success.
   bool ReadAttachment(base::PickleIterator* iter,
                       scoped_refptr<MessageAttachment>* attachment) const;
   // Returns true if there are any attachment in this message.
   bool HasAttachments() const;
   // Returns true if there are any MojoHandleAttachments in this message.
   bool HasMojoHandles() const;
   // Whether the message has any brokerable attachments.
   bool HasBrokerableAttachments() const;
 
+  void set_sender_pid(base::ProcessId id) { sender_pid_ = id; }
+  base::ProcessId get_sender_pid() const { return sender_pid_; }
+
 #ifdef IPC_MESSAGE_LOG_ENABLED
   // Adds the outgoing time from Time::Now() at the end of the message and sets
   // a bit to indicate that it's been added.
   void set_sent_time(int64 time);
   int64 sent_time() const;
 
   void set_received_time(int64 time) const;
   int64 received_time() const { return received_time_; }
   void set_output_params(const std::string& op) const { output_params_ = op; }
   const std::string& output_params() const { return output_params_; }
@@ skipping 59 matching lines @@
   void EnsureMessageAttachmentSet();
 
   MessageAttachmentSet* attachment_set() {
     EnsureMessageAttachmentSet();
     return attachment_set_.get();
   }
   const MessageAttachmentSet* attachment_set() const {
     return attachment_set_.get();
   }
 
+  // The process id of the sender of the message. This member is populated with
+  // a valid value for every message dispatched to listeners.
+  base::ProcessId sender_pid_;
+
 #ifdef IPC_MESSAGE_LOG_ENABLED
   // Used for logging.
   mutable int64 received_time_;
   mutable std::string output_params_;
   mutable LogData* log_data_;
   mutable bool dont_log_;
 #endif
 };
 
 //------------------------------------------------------------------------------
 
 }  // namespace IPC
 
 enum SpecialRoutingIDs {
   // indicates that we don't have a routing ID yet.
   MSG_ROUTING_NONE = -2,
 
   // indicates a general message not sent to a particular tab.
   MSG_ROUTING_CONTROL = kint32max,
 };
 
 #define IPC_REPLY_ID 0xFFFFFFF0  // Special message id for replies
 #define IPC_LOGGING_ID 0xFFFFFFF1  // Special message id for logging
 
 #endif  // IPC_IPC_MESSAGE_H_