Add xidle library to power_manager for testing how long the user has been idle

src/platform/power_manager/xidle-example.cc

+// Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <inttypes.h>
+#include <cstdio>
+#include "power_manager/xidle.h"
+
+int main(int argc, char *argv[]) {
+  chromeos::XIdle idle;
+  uint64 idleTime;
+  if (idle.getIdleTime(&idleTime)) {
+    printf("User has been idle for %" PRIu64 " milliseconds\n", idleTime);
+  } else {
+    printf("Cannot calculate idle time\n");
+  }
+  return 0;
+}