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 <avakulenko@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
diff --git a/omaha_request_params_unittest.cc b/omaha_request_params_unittest.cc
index 1daed1c..348e392 100644
--- a/omaha_request_params_unittest.cc
+++ b/omaha_request_params_unittest.cc
@@ -6,7 +6,7 @@
 
 #include <string>
 
-#include "base/file_util.h"
+#include "base/files/file_util.h"
 #include "gtest/gtest.h"
 #include "update_engine/constants.h"
 #include "update_engine/fake_system_state.h"