Source

File: wp-includes/class-wp-http-encoding.php

public static function should_decode( $headers ) {
		if ( is_array( $headers ) ) {
			if ( array_key_exists( 'content-encoding', $headers ) && ! empty( $headers['content-encoding'] ) ) {
				return true;
			}
		} elseif ( is_string( $headers ) ) {
			return ( stripos( $headers, 'content-encoding:' ) !== false );
		}

		return false;
	}