Merge ReliableQuicStream::WriteData with

Merge ReliableQuicStream::WriteData with
ReliableQuicStream::WriteOrBuffer, and make this method non-virtual.
It turns out the only cases where it was overridden could easily be
worked around.

Remove ReliableQuicStream::WriteDataInternal and use a MakeIovec helper
to work around it.  Rename ReliableQuicStream::WritevDataInternal to
ReliableQuicStream::WritevData.

Rename QuicStream::WritevData to QuicStream::Writev.

Cleanup of the various Write methods in ReliableQuicStream.

Merge internal change: 57753091

R=rch@chromium.org

[Ryan Hamilton, 2013-12-11 23:54:13]

lgtm