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

ipc/ipc_message.cc

 // 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.
 
 #include "ipc/ipc_message.h"
 
 #include "base/atomic_sequence_num.h"
 #include "base/logging.h"
 #include "build/build_config.h"
 #include "ipc/ipc_message_attachment.h"
@@ skipping 60 matching lines @@
   Init();
 }
 
 Message::Message(const Message& other) : base::Pickle(other) {
   Init();
   attachment_set_ = other.attachment_set_;
 }
 
 void Message::Init() {
   dispatch_error_ = false;
+  sender_pid_ = base::kNullProcessId;
 #ifdef IPC_MESSAGE_LOG_ENABLED
   received_time_ = 0;
   dont_log_ = false;
   log_data_ = NULL;
 #endif
 }
 
 Message& Message::operator=(const Message& other) {
   *static_cast<base::Pickle*>(this) = other;
   attachment_set_ = other.attachment_set_;
@@ skipping 64 matching lines @@
 bool Message::HasMojoHandles() const {
   return attachment_set_.get() && attachment_set_->num_mojo_handles() > 0;
 }
 
 bool Message::HasBrokerableAttachments() const {
   return attachment_set_.get() &&
          attachment_set_->num_brokerable_attachments() > 0;
 }
 
 }  // namespace IPC