gc benchmark: Update package list

Some old packages on the list were preventing this benchmark from working.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/820045

test/garbage/parser.go

@@ -118,6 +118,7 @@ var packages = []string{
 	"bignum",
 	"bufio",
 	"bytes",
+	"cmath",
 	"compress/flate",
 	"compress/gzip",
 	"compress/zlib",
@@ -127,13 +128,16 @@ var packages = []string{
 	"container/vector",
 	"crypto/aes",
 	"crypto/block",
+	"crypto/blowfish",
 	"crypto/hmac",
 	"crypto/md4",
 	"crypto/md5",
+	"crypto/rand",
 	"crypto/rc4",
 	"crypto/rsa",
 	"crypto/sha1",
 	"crypto/sha256",
+	"crypto/sha512",
 	"crypto/subtle",
 	"crypto/tls",
 	"crypto/x509",
@@ -154,9 +158,7 @@ var packages = []string{
 	"exp/datafmt",
 	"exp/draw",
 	"exp/eval",
-	"exp/exception",
 	"exp/iterable",
-	"exp/parser",
 	"expvar",
 	"flag",
 	"fmt",
@@ -170,6 +172,7 @@ var packages = []string{
 	"hash",
 	"hash/adler32",
 	"hash/crc32",
+	"hash/crc64",
 	"http",
 	"image",
 	"image/jpeg",
@@ -179,7 +182,9 @@ var packages = []string{
 	"json",
 	"log",
 	"math",
+	"mime",
 	"net",
+	"nntp",
 	"once",
 	"os",
 	"os/signal",
@@ -206,7 +211,7 @@ var packages = []string{
 	"time",
 	"unicode",
 	"utf8",
+	"utf16",
 	"websocket",
-	"xgb",
 	"xml",
 }