Use a direct include of strings headers in ash/.

BUG=247723
TEST=none
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Review URL: https://chromiumcodereview.appspot.com/16739005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@205277 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/ash/extended_desktop_unittest.cc b/ash/extended_desktop_unittest.cc
index d41f28a2..2a780f3 100644
--- a/ash/extended_desktop_unittest.cc
+++ b/ash/extended_desktop_unittest.cc
@@ -14,7 +14,7 @@
 #include "ash/wm/window_cycle_controller.h"
 #include "ash/wm/window_properties.h"
 #include "ash/wm/window_util.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/focus_client.h"