Update code to include base/files/file_util.h

file_util.h was moved from base to base/files
(https://codereview.chromium.org/468253002). This CL updates platform2
code to include base/files/file_util.h instead of base/file_util.h.

BUG=chromium:411001
TEST=Trybot run on paladin, release, and chromiumos-sdk builders.

Change-Id: I488925b54615e131e508a460dc1a27f88168f936
Reviewed-on: https://chromium-review.googlesource.com/216851
Reviewed-by: Alex Vakulenko <[email protected]>
Tested-by: Ben Chan <[email protected]>
Commit-Queue: Ben Chan <[email protected]>
diff --git a/postinstall_runner_action_unittest.cc b/postinstall_runner_action_unittest.cc
index d5e795e..1393a6f 100644
--- a/postinstall_runner_action_unittest.cc
+++ b/postinstall_runner_action_unittest.cc
@@ -11,7 +11,7 @@
 #include <string>
 #include <vector>
 
-#include <base/file_util.h>
+#include <base/files/file_util.h>
 #include <base/strings/string_util.h>
 #include <base/strings/stringprintf.h>
 #include <gtest/gtest.h>