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.cc

@@ -0,0 +1,90 @@
+// 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.
+//
+// $hash=fd0a4c1bd80a53778d6e40e4ebcd9d4484f91269$
+//
+
+#include "libcef_dll/ctocpp/shared_memory_region_ctocpp.h"
+#include "libcef_dll/shutdown_checker.h"
+
+// VIRTUAL METHODS - Body may be edited by hand.
+
+NO_SANITIZE("cfi-icall") bool CefSharedMemoryRegionCToCpp::IsValid() {
+  shutdown_checker::AssertNotShutdown();
+
+  cef_shared_memory_region_t* _struct = GetStruct();
+  if (CEF_MEMBER_MISSING(_struct, is_valid))
+    return false;
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  // Execute
+  int _retval = _struct->is_valid(_struct);
+
+  // Return type: bool
+  return _retval ? true : false;
+}
+
+NO_SANITIZE("cfi-icall") size_t CefSharedMemoryRegionCToCpp::Size() {
+  shutdown_checker::AssertNotShutdown();
+
+  cef_shared_memory_region_t* _struct = GetStruct();
+  if (CEF_MEMBER_MISSING(_struct, size))
+    return 0;
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  // Execute
+  size_t _retval = _struct->size(_struct);
+
+  // Return type: simple
+  return _retval;
+}
+
+NO_SANITIZE("cfi-icall") const void* CefSharedMemoryRegionCToCpp::Memory() {
+  shutdown_checker::AssertNotShutdown();
+
+  cef_shared_memory_region_t* _struct = GetStruct();
+  if (CEF_MEMBER_MISSING(_struct, memory))
+    return nullptr;
+
+  // Execute
+  const void* _retval = _struct->memory(_struct);
+
+  // Return type: simple
+  return _retval;
+}
+
+// CONSTRUCTOR - Do not edit by hand.
+
+CefSharedMemoryRegionCToCpp::CefSharedMemoryRegionCToCpp() {}
+
+// DESTRUCTOR - Do not edit by hand.
+
+CefSharedMemoryRegionCToCpp::~CefSharedMemoryRegionCToCpp() {
+  shutdown_checker::AssertNotShutdown();
+}
+
+template <>
+cef_shared_memory_region_t* CefCToCppRefCounted<
+    CefSharedMemoryRegionCToCpp,
+    CefSharedMemoryRegion,
+    cef_shared_memory_region_t>::UnwrapDerived(CefWrapperType type,
+                                               CefSharedMemoryRegion* c) {
+  NOTREACHED() << "Unexpected class type: " << type;
+  return nullptr;
+}
+
+template <>
+CefWrapperType CefCToCppRefCounted<CefSharedMemoryRegionCToCpp,
+                                   CefSharedMemoryRegion,
+                                   cef_shared_memory_region_t>::kWrapperType =
+    WT_SHARED_MEMORY_REGION;