Separates ipc code from common (http://crbug.com/16829)

ipc/ipc_descriptors.h

Index: ipc/ipc_descriptors.h
diff --git a/ipc/ipc_descriptors.h b/ipc/ipc_descriptors.h
new file mode 100644
index 0000000000000000000000000000000000000000..5717aa4e8f3983bb569ad9a323f57c1f613615f8
--- /dev/null
+++ b/ipc/ipc_descriptors.h
@@ -0,0 +1,14 @@
+// Copyright (c) 2009 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_DESCRIPTORS_H_
+#define IPC_IPC_DESCRIPTORS_H_
+
+// This is a list of global descriptor keys to be used with the
+// base::GlobalDescriptors object (see base/global_descriptors_posix.h)
+enum {
+  kPrimaryIPCChannel = 0,
+};
+
+#endif  // IPC_IPC_DESCRIPTORS_H_