update_engine: use base::NumberToString

base::XXXToString for number-string conversion has been unified to
base::NumberToString.

BUG=chromium:1054279
TEST=unittest

Change-Id: Ie47b1257df3492de660ea6d1c3fdf6e5cc8af791
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2210081
Reviewed-by: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Qijiang Fan <fqj@google.com>
Tested-by: Qijiang Fan <fqj@google.com>
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index 765af4f..e530de4 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -156,7 +156,7 @@
            version +
            "\">"
            "<packages><package hash=\"not-used\" name=\"" +
-           filename + "\" size=\"" + base::Int64ToString(size) +
+           filename + "\" size=\"" + base::NumberToString(size) +
            "\" hash_sha256=\"" + hash + "\"/>" +
            (multi_package ? "<package name=\"package2\" size=\"222\" "
                             "hash_sha256=\"hash2\"/>"