Cast: UDP socket operation should be more resilient

Cast: UDP socket operation should be more resilient

UDP socket has transient errors. In cast if we have an unsuccessful
read followed by an unsuccessful write then socket reading will stop.
This can cause the stream to be stopped until there is a successful
send again.

We should ignore any UDP socket errors and keep going.

Also changed the code location such that we start receiving
packets when CastTransportSender is created.

Testing

This change interacts directly with system UDP sockets so
it is not mockable. Instead I tested this locally with
streaming went smoothly.

BUG=396138

Review URL: https://codereview.chromium.org/409163003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286646 0039d316-1c4b-4281-b951-d872f2087c98