browser: fix a format string

The variable here is an `int64_t`. On arm, this should be `%lld`. PRId64
solves these things.

Bug: 1058218
Change-Id: Id06c379bd3af9498ea8b5e0fb94c2c594d4be1d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095942Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748793}

chrome/browser/download/notification/download_notification_browsertest.cc

@@ -209,7 +209,8 @@ class SlowDownloadInterceptor {
         "Cache-Control: max-age=0\n";
     headers += base::StringPrintf("Content-type: %s\n", mime_type.c_str());
     if (content_length >= 0) {
-      headers += base::StringPrintf("Content-Length: %ld\n", content_length);
+      headers +=
+          base::StringPrintf("Content-Length: %" PRId64 "\n", content_length);
       head->content_length = content_length;
     }
     head->headers = base::MakeRefCounted<net::HttpResponseHeaders>(