Add callbacks for unresponsive render process (fixes #3661)

The client can optionally wait or terminate the render process.

Expose process exit codes via OnRenderProcessTerminated and
CefGetExitCode (fixes #2126).

cefclient: Add a new https://tests/hang page for testing hang behavior.

cefclient: Move message and resource handling to a new BaseClientHandler
class to support loading of test pages in default Chrome UI windows.

libcef_dll/cpptoc/unresponsive_process_callback_cpptoc.cc

@@ -0,0 +1,82 @@
+// Copyright (c) 2024 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.
+//
+// $hash=d31cea8b172629a308a7d54f8dd6fccff4cc8823$
+//
+
+#include "libcef_dll/cpptoc/unresponsive_process_callback_cpptoc.h"
+#include "libcef_dll/shutdown_checker.h"
+
+namespace {
+
+// MEMBER FUNCTIONS - Body may be edited by hand.
+
+void CEF_CALLBACK unresponsive_process_callback_wait(
+    struct _cef_unresponsive_process_callback_t* self) {
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self) {
+    return;
+  }
+
+  // Execute
+  CefUnresponsiveProcessCallbackCppToC::Get(self)->Wait();
+}
+
+void CEF_CALLBACK unresponsive_process_callback_terminate(
+    struct _cef_unresponsive_process_callback_t* self) {
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self) {
+    return;
+  }
+
+  // Execute
+  CefUnresponsiveProcessCallbackCppToC::Get(self)->Terminate();
+}
+
+}  // namespace
+
+// CONSTRUCTOR - Do not edit by hand.
+
+CefUnresponsiveProcessCallbackCppToC::CefUnresponsiveProcessCallbackCppToC() {
+  GetStruct()->wait = unresponsive_process_callback_wait;
+  GetStruct()->terminate = unresponsive_process_callback_terminate;
+}
+
+// DESTRUCTOR - Do not edit by hand.
+
+CefUnresponsiveProcessCallbackCppToC::~CefUnresponsiveProcessCallbackCppToC() {
+  shutdown_checker::AssertNotShutdown();
+}
+
+template <>
+CefRefPtr<CefUnresponsiveProcessCallback>
+CefCppToCRefCounted<CefUnresponsiveProcessCallbackCppToC,
+                    CefUnresponsiveProcessCallback,
+                    cef_unresponsive_process_callback_t>::
+    UnwrapDerived(CefWrapperType type, cef_unresponsive_process_callback_t* s) {
+  DCHECK(false) << "Unexpected class type: " << type;
+  return nullptr;
+}
+
+template <>
+CefWrapperType
+    CefCppToCRefCounted<CefUnresponsiveProcessCallbackCppToC,
+                        CefUnresponsiveProcessCallback,
+                        cef_unresponsive_process_callback_t>::kWrapperType =
+        WT_UNRESPONSIVE_PROCESS_CALLBACK;