Move websocket creation to resource task

[nfallen]

This is a pull request for part of #6638

It includes the following changes:
-The websocket networking code (ie. making a connection, receiving data, and sending data) has been extracted out of components/script/dom/websocket.rs and into the new file components/net/websocket_loader.rs.
-websocket.rs now communicates with the resource task (components/net/resource_task.rs) to instruct it to initiate a new websocket connection

• websocket_loader.rs now provides an API sent over an IPCChannel that allows websocket.rs to receive feedback about this process and to subsequently send and receive data

[bors-servo]

☔ The latest upstream changes (presumably #8861) made this pull request unmergeable. Please resolve the merge conflicts.

[jdm]

This looks really great! There are a couple changes we can make for efficiency, but I'm really happy with how this PR turned out :D
-S-awaiting-review +S-needs-code-changes

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Reviewed 8 of 8 files at r1.
Review status: all files reviewed at latest revision, 8 unresolved discussions.

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components/net/resource_task.rs, line 180 [r1] (raw file):
I'm not clear on what this is asking.

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components/net/resource_task.rs, line 359 [r1] (raw file):
No need for mut here.

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components/net/websocket_loader.rs, line 45 [r1] (raw file):
Let's call this connect instead.

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components/net/websocket_loader.rs, line 57 [r1] (raw file):
Instead of creating these senders and receivers here and immediately sending them, we could create them in the DOM constructor and send the resource_action_receiver and resource_event_sender values as part of the initial connection request.

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components/net/websocket_loader.rs, line 120 [r1] (raw file):
Let's use while let Ok(dom_action) = resource_action_receiver.recv() { instead.

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components/script/dom/websocket.rs, line 143 [r1] (raw file):
I don't think we need the Arc<Mutex< anymore.

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components/script/dom/websocket.rs, line 239 [r1] (raw file):
We should be able to store this in self.sender immediatlely, rather than holding on to it for the ConnectionEstablishedTask later.

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components/servo/Cargo.lock, line 1159 [r1] (raw file):
We'll need to run ./mach update-cargo -p net in order to automatically update ports/cef/Cargo.lock and ports/gonk/Cargo.lock with these changes, too.

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Comments from the review on Reviewable.io

[nfallen]

Made a new commit with the updates so you can see the changes more easily, but I can squash the commits when the PR is ready!

[jdm]

One last change required - please squash the commits together while doing so, and I'll merge it :)
-S-awaiting-review +S-needs-code-changes +S-needs-squash

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Reviewed 6 of 6 files at r2.
Review status: all files reviewed at latest revision, 1 unresolved discussion.

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components/net/websocket_loader.rs, line 45 [r1] (raw file):
connect?

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Comments from the review on Reviewable.io

[Ms2ger]

@bors-servo r=jdm

[bors-servo]

📌 Commit e8c8277 has been approved by jdm

[bors-servo]

⌛ Testing commit e8c8277 with merge 951ab56...

[bors-servo]

☀️ Test successful - android, gonk, linux-dev, linux-rel, mac-dev-ref-unit, mac-rel-css, mac-rel-wpt