Add a shared memory variant of CefProcessMessage (fixes issue #3126)

CefSharedProcessMessageBuilder supports creation of a CefProcessMessage
backed by a CefSharedMemoryRegion.

Performance tests comparing the existing ArgumentList approach and the new
SharedMemoryRegion approach have been added to cefclient at
http://tests/ipc_performance.

CefMessageRouter has been updated to use SharedMemoryRegion as transport
for larger message payloads. The threshold is configurable via
|CefMessageRouterConfig.message_size_threshold|.

To test:
run `ceftests --gtest_filter=SendSharedProcessMessageTest.*:SharedProcessMessageTest.*:MessageRouterTest.Threshold*`

libcef_dll/ctocpp/shared_memory_region_ctocpp.h

@@ -0,0 +1,43 @@
+// Copyright (c) 2022 The Chromium Embedded Framework 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 file was generated by the CEF translator tool. If making changes by
+// hand only do so within the body of existing method and function
+// implementations. See the translator.README.txt file in the tools directory
+// for more information.
+//
+// $hash=d477b2660e271bbdc4d6e8f866f006b84f13e50d$
+//
+
+#ifndef CEF_LIBCEF_DLL_CTOCPP_SHARED_MEMORY_REGION_CTOCPP_H_
+#define CEF_LIBCEF_DLL_CTOCPP_SHARED_MEMORY_REGION_CTOCPP_H_
+#pragma once
+
+#if !defined(WRAPPING_CEF_SHARED)
+#error This file can be included wrapper-side only
+#endif
+
+#include "include/capi/cef_shared_memory_region_capi.h"
+#include "include/cef_shared_memory_region.h"
+#include "libcef_dll/ctocpp/ctocpp_ref_counted.h"
+
+// Wrap a C structure with a C++ class.
+// This class may be instantiated and accessed wrapper-side only.
+class CefSharedMemoryRegionCToCpp
+    : public CefCToCppRefCounted<CefSharedMemoryRegionCToCpp,
+                                 CefSharedMemoryRegion,
+                                 cef_shared_memory_region_t> {
+ public:
+  CefSharedMemoryRegionCToCpp();
+  virtual ~CefSharedMemoryRegionCToCpp();
+
+  // CefSharedMemoryRegion methods.
+  bool IsValid() override;
+  size_t Size() override;
+  const void* Memory() override;
+};
+
+#endif  // CEF_LIBCEF_DLL_CTOCPP_SHARED_MEMORY_REGION_CTOCPP_H_