Stub in more IPC attachment brokering functionality.

ipc/brokerable_attachment.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 "ipc/brokerable_attachment.h"
 
+#include "crypto/random.h"
+
 namespace IPC {
 
-BrokerableAttachment::BrokerableAttachment() {
+namespace {
+
+// In order to prevent mutually untrusted processes from stealing resources from
+// one another, the nonce must be secret. This generates a 128-bit,
+// cryptographicaly-strong random number.
+BrokerableAttachment::AttachmentId GetRandomId() {
+  BrokerableAttachment::AttachmentId id;
+  crypto::RandBytes(id.nonce, BrokerableAttachment::kNonceSize);
+  return id;
+}
+
+}  // namespace
+
+BrokerableAttachment::BrokerableAttachment() : id_(GetRandomId()) {
 }
 
 BrokerableAttachment::~BrokerableAttachment() {
 }
 
 BrokerableAttachment::AttachmentId BrokerableAttachment::GetIdentifier() const {
   return id_;
 }
 
+BrokerableAttachment::Type BrokerableAttachment::GetType() const {
+  return TYPE_BROKERABLE_ATTACHMENT;
+}
+
 }  // namespace IPC