Fix #include in run_testserver

This happens to show up on Fuchsia, but is a general IWYU for
base::DirectoryExists().

Bug: 808287
Change-Id: I26608991148aa2d381fe3f162a666a53722d4b57
Reviewed-on: https://chromium-review.googlesource.com/c/1298358
Reviewed-by: Asanka Herath <asanka@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602815}
diff --git a/net/tools/testserver/run_testserver.cc b/net/tools/testserver/run_testserver.cc
index 378d5b0..10ea873 100644
--- a/net/tools/testserver/run_testserver.cc
+++ b/net/tools/testserver/run_testserver.cc
@@ -7,6 +7,7 @@
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
+#include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"