GitLab

We were aggresively cancelling re-transmission before. This caused an
ill effect with duplicated ACKs that some packets are not transmitted.
This change adds a boolean to control whether or not to cancel rtx.

Review URL: https://codereview.chromium.org/322953004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276824 0039d316-1c4b-4281-b951-d872f2087c98