ipc: Update MachPortMac ownership semantics.

ipc/attachment_broker.h

Index: ipc/attachment_broker.h
diff --git a/ipc/attachment_broker.h b/ipc/attachment_broker.h
index 577d76219f9b5bb02f092b97886806c5fdb344d3..3f7a98c68692bb0a106f9955ecb7a670520120fc 100644
--- a/ipc/attachment_broker.h
+++ b/ipc/attachment_broker.h
@@ -63,7 +63,7 @@ class IPC_EXPORT AttachmentBroker : public Listener {
   // IPC::Channel to communicate with the broker process. This may be the same
   // IPC::Channel that is requesting the brokering of an attachment.
   // Returns true on success and false otherwise.
-  virtual bool SendAttachmentToProcess(const BrokerableAttachment* attachment,
+  virtual bool SendAttachmentToProcess(BrokerableAttachment* attachment,
                                        base::ProcessId destination_process) = 0;
 
   // Returns whether the attachment was available. If the attachment was