Add comments to HttpStreamParser::DoSendBody().
Add comments to HttpStreamParser::DoSendBody().

This function is relatively complex. Add comments to clarify
what this function does. Will clean up the code in a separate patch.

BUG=72001
TEST=chrome and tests build as before.


Review URL: http://codereview.chromium.org/9213018

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@118193 0039d316-1c4b-4281-b951-d872f2087c98

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