A change in #763 to address review comments caused problems. Originally,
instrumentedResponseWriter implemented the CloseNotifier interface, and
would panic if it was wrapping something that did not implement that
interface. This was split into a separate instrumentedResponseWriterCN
type that implements CloseNotifier, so there's a fallback if
instrumentedResponseWriter ever needs to wrap something that does not
implement this interface.
instrumentedResponseWriter's Value method would end up upcasting either
type back to instrumentedResponseWriter, which does not implement the
interface. In effect, instrumentedResponseWriterCN was never visible to
the handler.
This fixes the problem by implementing a wrapper Value method for
instrumentedResponseWriterCN.
Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
0e7462f1dd