Drain socket before throwing

[dnfield]

Fixes #78741
Similar to #78742

This makes it so that when a network image fails with a non-OK status code, we drain the socket to avoid keeping it open longer than necessary. Updates an existing test with this expectation.

Note that drain is documented as doing the same as what listen did in #78742, but just seems a bit more idiomatic to me.

Rather than creating a completely new test, I added an expectation to an existing test that exercised this code branch.

/cc @alexd6631

[jonahwilliams]

LGTM

[goderbauer]

LGTM

[alexd6631]

Hi @dnfield,

I agree that drain feels more idiomatic, I hesitated to use it in my previous MR.
Just a slight difference to note, is that in #78742 I used listen in order to explicitly silence errors that could arise when draining the response. With drain() I think an error will be thrown while awaiting the future, discarding the NetworkImageLoadException.

It may not be that important in practice, but I think this small behavior difference should be considered.

Best regards

[dnfield]

@alexd6631 I think that's ok. We're only throwing here to get into the evict logic in the catch block below. If there's truly a socket exception involved, then it'd be better to throw that more specific error than the generic one we're throwing.