Update to Chromium version 88.0.4324.0 (#827102)

- Mac: Xcode 12.2 and the MacOS 11.0 SDK are now required for building.
- MacOS 10.10 (Yosemite) is no longer supported (see https://crbug.com/1126056).
- Flash is no longer supported (see https://www.chromium.org/flash-roadmap).

libcef_dll/base/cef_callback_helpers.cc

@@ -1,40 +0,0 @@
-// Copyright 2013 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.
-
-#include "include/base/cef_callback_helpers.h"
-
-#include "include/base/cef_callback.h"
-
-namespace base {
-
-ScopedClosureRunner::ScopedClosureRunner() {}
-
-ScopedClosureRunner::ScopedClosureRunner(const Closure& closure)
-    : closure_(closure) {}
-
-ScopedClosureRunner::~ScopedClosureRunner() {
-  if (!closure_.is_null())
-    closure_.Run();
-}
-
-void ScopedClosureRunner::Reset() {
-  Closure old_closure = Release();
-  if (!old_closure.is_null())
-    old_closure.Run();
-}
-
-void ScopedClosureRunner::Reset(const Closure& closure) {
-  Closure old_closure = Release();
-  closure_ = closure;
-  if (!old_closure.is_null())
-    old_closure.Run();
-}
-
-Closure ScopedClosureRunner::Release() {
-  Closure result = closure_;
-  closure_.Reset();
-  return result;
-}
-
-}  // namespace base