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

ipc/ipc_channel_reader_unittest.cc

 // Copyright 2015 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 "build/build_config.h"
 
 #include <set>
 
 #include "ipc/attachment_broker.h"
 #include "ipc/brokerable_attachment.h"
@@ skipping 61 matching lines @@
   bool ShouldDispatchInputMessage(Message* msg) override { return true; }
 
   bool GetNonBrokeredAttachments(Message* msg) override { return true; }
 
   bool DidEmptyInputBuffers() override { return true; }
 
   void HandleInternalMessage(const Message& msg) override {}
 
   void DispatchMessage(Message* m) override { last_dispatched_message_ = m; }
 
+  base::ProcessId GetSenderPID() override { return base::kNullProcessId; }
+
   AttachmentBroker* GetAttachmentBroker() override { return broker_; }
 
   // This instance takes ownership of |m|.
   void AddMessageForDispatch(Message* m) {
     get_queued_messages()->push_back(m);
   }
 
   Message* get_last_dispatched_message() { return last_dispatched_message_; }
 
   void set_broker(AttachmentBroker* broker) { broker_ = broker; }
@@ skipping 36 matching lines @@
             reader.DispatchMessages());
   EXPECT_EQ(nullptr, reader.get_last_dispatched_message());
 
   broker.AddAttachment(attachment);
   EXPECT_EQ(m, reader.get_last_dispatched_message());
 }
 
 }  // namespace internal
 }  // namespace IPC
 #endif  // USE_ATTACHMENT_BROKER