Add simplest service/urlfetch implementation.

service/info/context.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 info
 
 import (
         "golang.org/x/net/context"
 )
 
@@ skipping 15 matching lines @@
 
 // getUnfiltered gets gets the Interface implementation from context without
 // any of the filters applied.
 func getUnfiltered(c context.Context) Interface {
         if f, ok := c.Value(infoKey).(Factory); ok && f != nil {
                 return f(c)
         }
         return nil
 }
 
-// Get gets gets the Interface implementation from context.
+// Get gets the Interface implementation from context.
 func Get(c context.Context) Interface {
         ret := getUnfiltered(c)
         if ret == nil {
                 return nil
         }
         for _, f := range getCurFilters(c) {
                 ret = f(c, ret)
         }
         return ret
 }
@@ skipping 23 matching lines @@
 func AddFilters(c context.Context, filts ...Filter) context.Context {
         if len(filts) == 0 {
                 return c
         }
         cur := getCurFilters(c)
         newFilts := make([]Filter, 0, len(cur)+len(filts))
         newFilts = append(newFilts, getCurFilters(c)...)
         newFilts = append(newFilts, filts...)
         return context.WithValue(c, infoFilterKey, newFilts)
 }