Update to current webrtc library

This is from the upstream library commit id
3326535126e435f1ba647885ce43a8f0f3d317eb, corresponding to Chromium
88.0.4290.1.

webrtc/rtc_base/zero_memory.cc

@@ -0,0 +1,38 @@
+/*
+ *  Copyright 2017 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#if defined(WEBRTC_WIN)
+#include <windows.h>
+#else
+#include <string.h>
+#endif
+
+#include "rtc_base/checks.h"
+#include "rtc_base/zero_memory.h"
+
+namespace rtc {
+
+// Code and comment taken from "OPENSSL_cleanse" of BoringSSL.
+void ExplicitZeroMemory(void* ptr, size_t len) {
+  RTC_DCHECK(ptr || !len);
+#if defined(WEBRTC_WIN)
+  SecureZeroMemory(ptr, len);
+#else
+  memset(ptr, 0, len);
+#if !defined(__pnacl__)
+  /* As best as we can tell, this is sufficient to break any optimisations that
+     might try to eliminate "superfluous" memsets. If there's an easy way to
+     detect memset_s, it would be better to use that. */
+  __asm__ __volatile__("" : : "r"(ptr) : "memory");  // NOLINT
+#endif
+#endif  // !WEBRTC_WIN
+}
+
+}  // namespace rtc