Make tracing work on Android

services/tracing/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("//mojo/public/mojo_application.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojo_native_application("tracing") {
   sources = [
     "main.cc",
     "trace_data_sink.cc",
     "trace_data_sink.h",
   ]
 
   deps = [
     ":bindings",
     "//base",
     "//mojo/application",
     "//mojo/common",
     "//mojo/public/cpp/application",
+    "//mojo/public/cpp/system",
   ]
 }
 
 mojom("bindings") {
   sources = [
     "tracing.mojom",
   ]
 }