Auto merge of #11544 - jdm:privatebrowsing, r=asajeffrey

Implement private browsing for mozbrowser

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Support the `mozprivatebrowsing` attribute on mozbrowser iframes. This separates the non-private and private sessions in terms of cookies, HSTS lists, cached HTTP credentials, HTTP connection pools, and web storage. The private session is shared between all private mozbrowsers, and lasts until shutdown.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] There are tests for these changes

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components/net_traits/lib.rs

@@ -39,7 +39,6 @@ use msg::constellation_msg::{PipelineId, ReferrerPolicy};
 use request::{Request, RequestInit};
 use response::{HttpsState, Response};
 use std::io::Error as IOError;
-use std::sync::mpsc::Sender;
 use std::thread;
 use storage_thread::StorageThreadMsg;
 use url::Url;
@@ -649,9 +648,10 @@ pub fn unwrap_websocket_protocol(wsp: Option<&header::WebSocketProtocol>) -> Opt
 #[derive(Clone, PartialEq, Eq, Copy, Hash, Debug, Deserialize, Serialize, HeapSizeOf)]
 pub struct ResourceId(pub u32);
 
+#[derive(Deserialize, Serialize)]
 pub enum ConstellationMsg {
     /// Queries whether a pipeline or its ancestors are private
-    IsPrivate(PipelineId, Sender<bool>),
+    IsPrivate(PipelineId, IpcSender<bool>),
 }
 
 /// Network errors that have to be exported out of the loaders