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*`

include/cef_shared_process_message_builder.h

@@ -0,0 +1,87 @@
+// Copyright (c) 2022 Marshall A. Greenblatt. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the name Chromium Embedded
+// Framework nor the names of its contributors may be used to endorse
+// or promote products derived from this software without specific prior
+// written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// ---------------------------------------------------------------------------
+//
+// The contents of this file must follow a specific format in order to
+// support the CEF translator tool. See the translator.README.txt file in the
+// tools directory for more information.
+//
+
+#ifndef CEF_INCLUDE_CEF_SHARED_PROCESS_MESSAGE_BUILDER_H_
+#define CEF_INCLUDE_CEF_SHARED_PROCESS_MESSAGE_BUILDER_H_
+#pragma once
+
+#include "include/cef_process_message.h"
+
+///
+// Class that builds a CefProcessMessage containing a shared memory region.
+// This class is not thread-safe but may be used exclusively on a different
+// thread from the one which constructed it.
+///
+/*--cef(source=library)--*/
+class CefSharedProcessMessageBuilder : public virtual CefBaseRefCounted {
+ public:
+  ///
+  // Creates a new CefSharedProcessMessageBuilder with the specified |name| and
+  // shared memory region of specified |byte_size|.
+  ///
+  /*--cef()--*/
+  static CefRefPtr<CefSharedProcessMessageBuilder> Create(const CefString& name,
+                                                          size_t byte_size);
+  ///
+  // Returns true if the builder is valid.
+  ///
+  /*--cef()--*/
+  virtual bool IsValid() = 0;
+
+  ///
+  // Returns the size of the shared memory region in bytes. Returns 0 for
+  // invalid instances.
+  ///
+  /*--cef()--*/
+  virtual size_t Size() = 0;
+
+  ///
+  // Returns the pointer to the writable memory. Returns nullptr for invalid
+  // instances. The returned pointer is only valid for the life span of this
+  // object.
+  ///
+  /*--cef()--*/
+  virtual void* Memory() = 0;
+
+  ///
+  // Creates a new CefProcessMessage from the data provided to the builder.
+  // Returns nullptr for invalid instances. Invalidates the builder instance.
+  ///
+  /*--cef()--*/
+  virtual CefRefPtr<CefProcessMessage> Build() = 0;
+};
+
+#endif  // CEF_INCLUDE_CEF_SHARED_PROCESS_MESSAGE_BUILDER_H_