Export headers from /_log when requesting YAML

This got lost in the refactoring, now it's back.

go/fake-http/fake-http.go

@@ -270,11 +270,18 @@ type LogEntry struct {
// AsResponse returns a Response representation of the entry.
func (e LogEntry) AsResponse() Response {
	headers := make([]Header, 0, len(e.response.Header))
	for name, vals := range e.response.Header {
		for _, val := range vals {
			headers = append(headers, Header{Name: name, Value: val})
		}
	}
	return Response{
		Method: e.request.Method,
		Path:   e.request.URL.Path,
		Status: e.response.StatusCode,
		Body:   e.responseBody.String(),
		Method:  e.request.Method,
		Path:    e.request.URL.Path,
		Status:  e.response.StatusCode,
		Headers: headers,
		Body:    e.responseBody.String(),
	}
}