Add a small untility for checking to see if the X server is alive.

tools/xdisplaycheck/xdisplaycheck.cc

+// Copyright (c) 2009 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.
+//
+// This is a small program that tries to connect to the X server.  It
+// continually retries until it connects or 5 seconds pass.  If it fails
+// to connect to the X server after 5 seconds, it returns an error code
+// of -1.
+//
+// This is to help verify that the X server is available before we start
+// start running tests on the build bots.
+
+#include <errno.h>
+#include <stdio.h>
+#include <time.h>
+#include <X11/Xlib.h>
+
+void Sleep(int duration_ms) {
+  struct timespec sleep_time, remaining;
+
+  // Contains the portion of duration_ms >= 1 sec.
+  sleep_time.tv_sec = duration_ms / 1000;
+  duration_ms -= sleep_time.tv_sec * 1000;
+
+  // Contains the portion of duration_ms < 1 sec.
+  sleep_time.tv_nsec = duration_ms * 1000 * 1000;  // nanoseconds.
+
+  while (nanosleep(&sleep_time, &remaining) == -1 && errno == EINTR)
+    sleep_time = remaining;
+}
+
+int main(int argc, char* argv[]) {
+  int kNumTries = 50;
+  for (int i = 0; i < kNumTries; ++i) {
+    Display* display = XOpenDisplay(NULL);
+    if (display)
+      return 0;
+    Sleep(100);
+  }
+
+  printf("Failed to connect to %s\n", XDisplayName(NULL));
+  return -1;
+}