Reland #2 "ipc: Add a new field num_brokered_attachments to the message header."

ipc/ipc_channel.h

Index: ipc/ipc_channel.h
diff --git a/ipc/ipc_channel.h b/ipc/ipc_channel.h
index 4784a5cac2f80c491ef27ab01aae9c07431ae341..06555d333de03dc565a8bed0d25a75461577eca2 100644
--- a/ipc/ipc_channel.h
+++ b/ipc/ipc_channel.h
@@ -169,6 +169,11 @@ class IPC_EXPORT Channel : public Endpoint {
 
   ~Channel() override;
 
+  // TODO(erikchen): Temporary code to help track http://crbug.com/527588.
+  using MessageVerifier = void (*)(const Message*);
+  static void SetMessageVerifier(MessageVerifier verifier);
+  static MessageVerifier GetMessageVerifier();
+
   // Connect the pipe.  On the server side, this will initiate
   // waiting for connections.  On the client, it attempts to
   // connect to a pre-existing pipe.  Note, calling Connect()