Implicitly emitted header disappears when it is evicted from header table

[tatsuhiro-t]

We say that "implicitly emitted" if the header is common between the current header set and previous header set, which means that it is in the reference set and not actually emitted byte code. When such entry is evicted from header table, it is also removed from reference set. The end effect is that the decoder misses such header.

It is easily reproducible. Just add new relatively big header value in each round trip. You will see ":scheme" disappears from the decoder output.

There are several ways to fix this issue. The one way is that whenever such header is removed from the header table, emit indexed representation twice before removal.

I think this is one of the tricky part of the current spec, to handle common headers.

[akalin-chromium]

Thanks! Should be fixed as of 142afbc.