Added support for Haystack tracing

vendor/github.com/ExpediaDotCom/haystack-client-go/logger.go

@@ -0,0 +1,37 @@
+/*
+ *  Copyright 2018 Expedia Group.
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ *
+ */
+
+package haystack
+
+/*Logger defines a new logger interface*/
+type Logger interface {
+	Info(format string, v ...interface{})
+	Error(format string, v ...interface{})
+	Debug(format string, v ...interface{})
+}
+
+/*NullLogger does nothing*/
+type NullLogger struct{}
+
+/*Error prints the error message*/
+func (logger NullLogger) Error(format string, v ...interface{}) {}
+
+/*Info prints the info message*/
+func (logger NullLogger) Info(format string, v ...interface{}) {}
+
+/*Debug prints the info message*/
+func (logger NullLogger) Debug(format string, v ...interface{}) {}