Repair two DCHECKS

In one case, the packet was seemingly buffered, and then discarded, but
asynchronously sent (needlessly). We can just return, and not
track the packet since it definately won't have its contents
retransmitted.

In the other case it appears that the packet was sent, containing a
retransmission of previously sent frames.  Unfortunately that resend
was write-blocked, and while waiting, the original packet was acked,
which lead to removing the list of retransmittable frames from that
latter (write-blocked) packet.  An assertion was then failing when
the packet was sent, as it was expected to be retransmittable, but
had no retransmittable frames.

R=ian,rch
BUG=332631

Review URL: https://codereview.chromium.org/133243002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244129 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244129