exo: Fix CreateLinuxFence test.

components/exo/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 source_set("exo") {
   sources = [
     "buffer.cc",
@@ skipping 118 matching lines @@
     "//ui/aura",
     "//ui/events:dom_keycode_converter",
     "//ui/events:test_support",
     "//ui/gfx",
     "//ui/keyboard",
     "//ui/message_center",
     "//ui/views",
     "//ui/wm:wm",
   ]
 
+  if (is_linux) {
+    deps += [ "//third_party/libsync:libsync" ]
+  }
+
   if (use_ozone) {
     deps += [ "//ui/ozone" ]
   }
 }
 
 test("exo_unittests") {
   sources = [
     "test/run_all_unittests.cc",
   ]
 
@@ skipping 13 matching lines @@
   ]
 
   if (use_x11) {
     deps += [ "//tools/xdisplaycheck" ]
   }
 
   if (is_linux) {
     deps += [ "//components/exo/wayland:unit_tests" ]
   }
 }