Do not emit indexed header fields first in HpackEncoder.

Do not emit indexed header fields first in HpackEncoder.

In HpackEncoder, do not emit regular headers that can be found in the dynamic
table before the ones that cannot in fear of evicting one that could have been
indexed.  Instead, go through the header fields "in order".

Note that since HpackEncoder takes the header block as a map, order is still not
guaranteed.  In particular, different keys will be sorted alphabetically.
However, this change guarantees order of headers with identical keys.  Such
headers are passed as "key: value0\0value1" to HpackEncoder, but sent as two
separate header fields "key: value0" and "key: value1" on the wire.  Before this
CL, order could have got changed depending on which fields were in the dynamic
table.

This CL lands server side change 82356409 by bnc.

BUG=443570
Committed: https://crrev.com/540eba1e09561a3ba2ff663e26607d7bfc1397b5
Cr-Commit-Position: refs/heads/master@{#309064}

[Bence, 2014-12-18 16:15:51]

bnc@chromium.org changed reviewers:
+ rch@chromium.org

[Bence, 2014-12-18 16:15:52]

Ryan: I'd like to land this today so that it could be merged to 40 this year. 
PTAL at your earliest convenience.  Thanks.

[Ryan Hamilton, 2014-12-18 19:13:18]

lgtm

[Bence, 2014-12-18 19:15:02]

The CQ bit was checked by bnc@chromium.org

[commit-bot: I haz the power, 2014-12-18 19:16:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/803843004/1

[commit-bot: I haz the power, 2014-12-18 20:13:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-18 20:14:29]

Patchset 1 (id:??) landed as
https://crrev.com/540eba1e09561a3ba2ff663e26607d7bfc1397b5
Cr-Commit-Position: refs/heads/master@{#309064}