Update GCS storage library to support GetObject API on gzipped objects (#6506)

Fixes #6280

vendor/google.golang.org/api/transport/http/go18.go

@@ -0,0 +1,31 @@
+// Copyright 2018 Google LLC
+//
+// 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.
+
+// +build go1.8
+
+package http
+
+import (
+	"net/http"
+
+	"contrib.go.opencensus.io/exporter/stackdriver/propagation"
+	"go.opencensus.io/plugin/ochttp"
+)
+
+func addOCTransport(trans http.RoundTripper) http.RoundTripper {
+	return &ochttp.Transport{
+		Base:        trans,
+		Propagation: &propagation.HTTPFormat{},
+	}
+}