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/cpptoc/shared_memory_region_cpptoc.cc

@@ -0,0 +1,105 @@
+// 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.
+//
+// $hash=b8c6bf91bf16cb696121e7d304c21fbcdc927ffd$
+//
+
+#include "libcef_dll/cpptoc/shared_memory_region_cpptoc.h"
+#include "libcef_dll/shutdown_checker.h"
+
+namespace {
+
+// MEMBER FUNCTIONS - Body may be edited by hand.
+
+int CEF_CALLBACK
+shared_memory_region_is_valid(struct _cef_shared_memory_region_t* self) {
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return 0;
+
+  // Execute
+  bool _retval = CefSharedMemoryRegionCppToC::Get(self)->IsValid();
+
+  // Return type: bool
+  return _retval;
+}
+
+size_t CEF_CALLBACK
+shared_memory_region_size(struct _cef_shared_memory_region_t* self) {
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return 0;
+
+  // Execute
+  size_t _retval = CefSharedMemoryRegionCppToC::Get(self)->Size();
+
+  // Return type: simple
+  return _retval;
+}
+
+const void* CEF_CALLBACK
+shared_memory_region_memory(struct _cef_shared_memory_region_t* self) {
+  shutdown_checker::AssertNotShutdown();
+
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return 0;
+
+  // Execute
+  const void* _retval = CefSharedMemoryRegionCppToC::Get(self)->Memory();
+
+  // Return type: simple
+  return _retval;
+}
+
+}  // namespace
+
+// CONSTRUCTOR - Do not edit by hand.
+
+CefSharedMemoryRegionCppToC::CefSharedMemoryRegionCppToC() {
+  GetStruct()->is_valid = shared_memory_region_is_valid;
+  GetStruct()->size = shared_memory_region_size;
+  GetStruct()->memory = shared_memory_region_memory;
+}
+
+// DESTRUCTOR - Do not edit by hand.
+
+CefSharedMemoryRegionCppToC::~CefSharedMemoryRegionCppToC() {
+  shutdown_checker::AssertNotShutdown();
+}
+
+template <>
+CefRefPtr<CefSharedMemoryRegion> CefCppToCRefCounted<
+    CefSharedMemoryRegionCppToC,
+    CefSharedMemoryRegion,
+    cef_shared_memory_region_t>::UnwrapDerived(CefWrapperType type,
+                                               cef_shared_memory_region_t* s) {
+  NOTREACHED() << "Unexpected class type: " << type;
+  return nullptr;
+}
+
+template <>
+CefWrapperType CefCppToCRefCounted<CefSharedMemoryRegionCppToC,
+                                   CefSharedMemoryRegion,
+                                   cef_shared_memory_region_t>::kWrapperType =
+    WT_SHARED_MEMORY_REGION;