test/bench/go1: use raw string instead of string addition

to reduce compile time memory/stack usage.
Update #4970
$ go test -c ../test/bench/go1
before:
0.36user 0.07system 0:00.44elapsed 100%CPU
(0avgtext+0avgdata 540720maxresident)k
0inputs+19840outputs (0major+56451minor)pagefaults 0swaps
after:
0.33user 0.05system 0:00.39elapsed 100%CPU
(0avgtext+0avgdata 289936maxresident)k
0inputs+19864outputs (0major+29615minor)pagefaults 0swaps

And stack usage is reduced to below 1MiB.

R=golang-dev, r, dave
CC=golang-dev
https://golang.org/cl/7436050

test/bench/go1/json_test.go

@@ -7,12 +7,12 @@
 package go1
 
 import (
+	"bytes"
 	"compress/bzip2"
 	"encoding/base64"
 	"encoding/json"
 	"io"
 	"io/ioutil"
-	"strings"
 	"testing"
 )
 
@@ -23,7 +23,7 @@ var (
 
 func makeJsonBytes() []byte {
 	var r io.Reader
-	r = strings.NewReader(jsonbz2_base64)
+	r = bytes.NewReader(bytes.Replace(jsonbz2_base64, []byte{'\n'}, nil, -1))
 	r = base64.NewDecoder(base64.StdEncoding, r)
 	r = bzip2.NewReader(r)
 	b, err := ioutil.ReadAll(r)