Implement navigator.sendBeacon()

LayoutTests/http/tests/navigation/resources/check-beacon.php

+<?php
+$beaconFilename = "beacon" . (isset($_REQUEST['name']) ? $_REQUEST['name'] : "") . ".txt";
+$retries = isset($_REQUEST['retries']) ? (int)$_REQUEST['retries'] : -1;
+while (!file_exists($beaconFilename) && $retries != 0) {
+    usleep(10000);
+    # file_exists() caches results, we want to invalidate the cache.
+    clearstatcache();
+    $retries--;
+}
+
+header('Content-Type: text/plain');
+header('Access-Control-Allow-Origin: *');
+if (file_exists($beaconFilename)) {
+    echo "Beacon sent successfully\n";
+    $beaconFile = fopen($beaconFilename, 'r');
+    while ($line = fgets($beaconFile)) {
+        $trimmed = trim($line);
+        if ($trimmed != "")
+            echo "$trimmed\n";
+    }
+    fclose($beaconFile);
+    unlink($beaconFilename);
+} else {
+    echo "Beacon not sent\n";
+}
+?>