Frame identifiers have changed from int64_t to string type. This is due
to https://crbug.com/1502660 which removes access to frame routing IDs
in the renderer process. New cross-process frame identifiers are 160-bit
values (32-bit child process ID + 128-bit local frame token) and most
easily represented as strings. All other frame-related expectations and
behaviors remain the same.
Known issues:
- The CefLoadCRLSetsFile function needs to be re-implemented (see issue #2497).
- Linux: GTK2 support has been removed. The cefclient sample needs to be updated
to use GTK3 (see issue #2014).