Replace macros with C++17 features (see issue #3362)

- Convert ALLOW_UNUSED_LOCAL to [[maybe_unused]]
- Convert WARN_UNUSED_RESULT to [[nodiscard]]

include/wrapper/cef_scoped_temp_dir.h

@@ -71,23 +71,23 @@ class CefScopedTempDir {
   // Creates a unique directory in TempPath, and takes ownership of it.
   // See file_util::CreateNewTemporaryDirectory.
   ///
-  bool CreateUniqueTempDir() WARN_UNUSED_RESULT;
+  [[nodiscard]] bool CreateUniqueTempDir();
 
   ///
   // Creates a unique directory under a given path, and takes ownership of it.
   ///
-  bool CreateUniqueTempDirUnderPath(const CefString& path) WARN_UNUSED_RESULT;
+  [[nodiscard]] bool CreateUniqueTempDirUnderPath(const CefString& path);
 
   ///
   // Takes ownership of directory at |path|, creating it if necessary.
   // Don't call multiple times unless Take() has been called first.
   ///
-  bool Set(const CefString& path) WARN_UNUSED_RESULT;
+  [[nodiscard]] bool Set(const CefString& path);
 
   ///
   // Deletes the temporary directory wrapped by this object.
   ///
-  bool Delete() WARN_UNUSED_RESULT;
+  [[nodiscard]] bool Delete();
 
   ///
   // Caller takes ownership of the temporary directory so it won't be destroyed