Add ozone_unittests to the build.

BUILD.gn

 # Copyright 2014 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")
 
 # This target will be built if no target is specified when invoking ninja.
 group("default") {
   testonly = true
 
@@ skipping 15 matching lines @@
       "//sandbox/linux:sandbox",
       "//sandbox/linux:sandbox_linux_unittests",
       "//tools/xdisplaycheck",
     ]
   }
 
   if (use_ozone) {
     deps += [
       "//ui/ozone",
       "//ui/ozone/demo",
+      "//ui/ozone:ozone_unittests",
     ]
   }
 }
 
 # Deprecated name for the default build target.
 group("root") {
   testonly = true
   deps = [
     ":default",
   ]
 }