Called on the IO thread to handle requests for URLs with an unknown
protocol component. The |browser| and |frame| values represent the source
of the request, and may be NULL for requests originating from service
workers or cef_urlrequest_t. |request| cannot be modified in this
callback. Set |allow_os_execution| to true (1) to attempt execution via
the registered OS protocol handler, if any. SECURITY WARNING: YOU SHOULD
USE THIS METHOD TO ENFORCE RESTRICTIONS BASED ON SCHEME, HOST OR OTHER URL
ANALYSIS BEFORE ALLOWING OS EXECUTION.
Called on the IO thread to handle requests for URLs with an unknown protocol component. The |browser| and |frame| values represent the source of the request, and may be NULL for requests originating from service workers or cef_urlrequest_t. |request| cannot be modified in this callback. Set |allow_os_execution| to true (1) to attempt execution via the registered OS protocol handler, if any. SECURITY WARNING: YOU SHOULD USE THIS METHOD TO ENFORCE RESTRICTIONS BASED ON SCHEME, HOST OR OTHER URL ANALYSIS BEFORE ALLOWING OS EXECUTION.