The change to the unit test is necessary because the resource thread is not
resilient against either of these Senders being dropped while the resource
thread is running. Before this change, it held clones of those senders itself
(public_setup_chan_clone, private_setup_chan_clone).
In most scenarios, where the user of Servo will not override the default
user agent, the user agent can be a `&'static str`. But since we allow
for customization, we currently use a `String` to represent the user
agent. This commit migrates the user agent to be represented as a
`Cow<'static, str>`, which (at the cost of ergonomics) prevents
unnecessary allocations whenever cloning the user agent string in the
scenario the user doesn't override the user agent.
Changes include:
- Introduce an IpcSend trait to abstract over a collection of IpcSenders
- Implement ResourceThreads collection to abstract the resource-related
sub threads across the component
- Rename original ResourceThread and ControlMsg into an unifed CoreResource__
to accommodate above changes and avoid confusions
add pass-through from doc to http-loader for referrer_policy, ref_URL
add logic for setting referer header
add script pass-through for referrer
add unit tests for setting referer header
In rust-url 1.0 the `Url` struct is going to have private fields, and there
is no way to to create an aribitrary one without going through the parser.
The plugin never had a clear demonstrated performance benefit,
it was made mostly because it was possible and relatively easy at the time.
