Fix GS client breakage, remove offset hacks.

common/gcloud/gs/opts.go

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-package gs
-
-import (
-        "fmt"
-        "net/http"
-)
-
-// Options are the set of extra options to apply to the Google Storage request.
-type Options struct {
-        // From is the range request starting index. If >0, the beginning of the
-        // range request will be set.
-        From int64
-        // To is the range request ending index. If >0, the end of the
-        // range request will be set.
-        //
-        // If no From index is set, this will result in a request indexed from the end
-        // of the object.
-        To int64
-}
-
-// gsRoundTripper is an http.RoundTripper implementation that allows us to
-// inject some HTTP headers. It is necessary because the stock Google Storage
-// API doesn't allow access to specific header manipulation.
-//
-// https://cloud.google.com/storage/docs/reference-headers#range
-type gsRoundTripper struct {
-        http.RoundTripper
-        *Options
-}
-
-func (rt *gsRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
-        if req.Header == nil {
-                req.Header = make(http.Header)
-        }
-
-        // Add Range header, if configured.
-        rh := ""
-        switch {
-        case rt.From > 0 && rt.To > 0:
-                rh = fmt.Sprintf("bytes=%d-%d", rt.From, rt.To)
-
-        case rt.From > 0:
-                rh = fmt.Sprintf("bytes=%d-", rt.From)
-
-        case rt.To > 0:
-                rh = fmt.Sprintf("bytes=-%d", rt.To)
-        }
-        if rh != "" {
-                req.Header.Add("Range", rh)
-        }
-
-        return rt.RoundTripper.RoundTrip(req)
-}