macOS: Load the CEF framework using dlopen instead of direct linking (issue #2459)

This is a prerequisite for using the Chromium V2 sandbox.

libcef_dll/wrapper/cef_library_loader_mac.mm

@@ -0,0 +1,77 @@
+// Copyright (c) 2018 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.
+
+#include "include/wrapper/cef_library_loader.h"
+
+#include <libgen.h>
+#include <mach-o/dyld.h>
+#include <stdio.h>
+
+#include <memory>
+#include <sstream>
+
+namespace {
+
+const char kFrameworkPath[] =
+    "Chromium Embedded Framework.framework/Chromium Embedded Framework";
+const char kPathFromHelperExe[] = "../../..";
+const char kPathFromMainExe[] = "../Frameworks";
+
+std::string GetFrameworkPath(bool helper) {
+  uint32_t exec_path_size = 0;
+  int rv = _NSGetExecutablePath(NULL, &exec_path_size);
+  if (rv != -1) {
+    return std::string();
+  }
+
+  std::unique_ptr<char[]> exec_path(new char[exec_path_size]);
+  rv = _NSGetExecutablePath(exec_path.get(), &exec_path_size);
+  if (rv != 0) {
+    return std::string();
+  }
+
+  // Get the directory path of the executable.
+  const char* parent_dir = dirname(exec_path.get());
+  if (!parent_dir) {
+    return std::string();
+  }
+
+  // Append the relative path to the framework.
+  std::stringstream ss;
+  ss << parent_dir << "/" << (helper ? kPathFromHelperExe : kPathFromMainExe)
+     << "/" << kFrameworkPath;
+  return ss.str();
+}
+
+}  // namespace
+
+CefScopedLibraryLoader::CefScopedLibraryLoader() : loaded_(false) {}
+
+bool CefScopedLibraryLoader::Load(bool helper) {
+  if (loaded_) {
+    return false;
+  }
+
+  const std::string& framework_path = GetFrameworkPath(helper);
+  if (framework_path.empty()) {
+    fprintf(stderr, "App does not have the expected bundle structure.\n");
+    return false;
+  }
+
+  // Load the CEF framework library.
+  if (!cef_load_library(framework_path.c_str())) {
+    fprintf(stderr, "Failed to load the CEF framework.\n");
+    return false;
+  }
+
+  loaded_ = true;
+  return true;
+}
+
+CefScopedLibraryLoader::~CefScopedLibraryLoader() {
+  if (loaded_) {
+    // Unload the CEF framework library.
+    cef_unload_library();
+  }
+}