Land Recent QUIC changes.
Move the QuicPacketWriter to the QuicConnection from the Helper. Also
changes the TestWriters to wrap another writer, instead of
re-implementing the default writer logic.
Merge internal change:
53858038
Adding an end to end test to simulate the socket being write blocked 10%
of the time.
Merge internal change:
53813433
R=rch@chromium.org
Review URL: https://codereview.chromium.org/
37733002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230566 0039d316-1c4b-4281-b951-d872f2087c98