Remove HpackHuffmanAggregator.

Remove HpackHuffmanAggregator.

Remove HpackHuffmanAggregator header, implementation, test, and build rules.
Obsolete Net.SpdyHpackEncoddeCharacterFrequency histogram.  As the HTTP/2
standard is finalized, there is no longer a need to gather character
distribution statistics.

BUG=414758
Committed: https://crrev.com/cc9f081bcbb746dce011636b7fff769a19619f06
Cr-Commit-Position: refs/heads/master@{#322467}

[Bence, 2015-03-26 14:45:44]

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

[Bence, 2015-03-26 14:45:44]

Ryan, PTAL.  Thanks.

[Ryan Hamilton, 2015-03-26 19:13:48]

lgtm

[Bence, 2015-03-26 20:12:49]

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

[Bence, 2015-03-26 20:12:49]

Ilya: please review changes in tools/metrics/histograms/histograms.xml.  Thank
you.

[Ilya Sherman, 2015-03-26 20:55:43]

histograms.xml lgtm

[Bence, 2015-03-26 20:59:57]

The CQ bit was checked by bnc@chromium.org

[commit-bot: I haz the power, 2015-03-26 21:00:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1017853004/1

[commit-bot: I haz the power, 2015-03-26 21:04:04]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-26 21:05:06]

Patchset 1 (id:??) landed as
https://crrev.com/cc9f081bcbb746dce011636b7fff769a19619f06
Cr-Commit-Position: refs/heads/master@{#322467}