constellation: crash to a new “sad tab” error page (#30290)

* constellation: crash to a new “sad tab” page

* check in resources/crash.html

* use a separate enum variant instead of keying on reason

* fmt + tidy

* rename Resource::Crash to Resource::CrashHTML

* clean up crash page and add details (reason + backtrace)

* avoid repeating crash errors in script::script_thread warn log

* make new LoadData init more idiomatic

* clarify comments and new fields

* fix doc comment style

components/net_traits/lib.rs

@@ -758,8 +758,10 @@ pub enum NetworkError {
     /// Could be any of the internal errors, like unsupported scheme, connection errors, etc.
     Internal(String),
     LoadCancelled,
-    /// SSL validation error that has to be handled in the HTML parser
+    /// SSL validation error, to be converted to Resource::BadCertHTML in the HTML parser.
     SslValidation(String, Vec<u8>),
+    /// Crash error, to be converted to Resource::Crash in the HTML parser.
+    Crash(String),
 }
 
 impl NetworkError {

components/net_traits/request.rs

@@ -254,6 +254,8 @@ pub struct RequestBuilder {
     pub initiator: Initiator,
     pub https_state: HttpsState,
     pub response_tainting: ResponseTainting,
+    /// Servo internal: if crash details are present, trigger a crash error page with these details.
+    pub crash: Option<String>,
 }
 
 impl RequestBuilder {
@@ -284,6 +286,7 @@ impl RequestBuilder {
             csp_list: None,
             https_state: HttpsState::None,
             response_tainting: ResponseTainting::Basic,
+            crash: None,
         }
     }
 
@@ -382,6 +385,11 @@ impl RequestBuilder {
         self
     }
 
+    pub fn crash(mut self, crash: Option<String>) -> Self {
+        self.crash = crash;
+        self
+    }
+
     pub fn build(self) -> Request {
         let mut request = Request::new(
             self.url.clone(),
@@ -415,6 +423,7 @@ impl RequestBuilder {
         request.parser_metadata = self.parser_metadata;
         request.csp_list = self.csp_list;
         request.response_tainting = self.response_tainting;
+        request.crash = self.crash;
         request
     }
 }
@@ -488,6 +497,8 @@ pub struct Request {
     #[ignore_malloc_size_of = "Defined in rust-content-security-policy"]
     pub csp_list: Option<CspList>,
     pub https_state: HttpsState,
+    /// Servo internal: if crash details are present, trigger a crash error page with these details.
+    pub crash: Option<String>,
 }
 
 impl Request {
@@ -528,6 +539,7 @@ impl Request {
             response_tainting: ResponseTainting::Basic,
             csp_list: None,
             https_state: https_state,
+            crash: None,
         }
     }