After issue 554220 is completed, exactly one of the following can happen to any stream pushed on an HTTP/2 connection:
* the pushed stream is rejected when received (for example, because of invalid scheme or method);
* the pushed stream is rejected when a request is generated because the pushed response headers have not been received yet;
* the pushed stream is rejected when the pushed response headers are received (for example, because the response is 206 Partial Range);
* the pushed stream is rejected when a request is generated because the pushed response headers do not match the request headers (for example, because of Vary header);
* the pushed stream is matched with a request;
* the pushed stream is never matched with a request and is reset after a timeout.

A histogram is needed with these buckets that is recorded exactly once for every pushed stream.