Move code related to json packet reading to JsonPacketSender trait

fixup! Move code related to json packet reading to JsonPacketSender trait
auto merge of #3955 : thiagopnts/servo/devtools-refactoring, r=jdm

I was messing around devtools code and saw some TODOs, is anyone working on it? I took one of them:

```// TODO: this really belongs in the protocol module.```

I would be glad to help with this if no one is on it already, just let me know.
Rust upgrade to rustc hash b03a2755193cd756583bcf5831cf4545d75ecb8a
Fix unit test compile error.
Fix CEF build cargo.lock file