script: Implement support for X-Frame-Options (#43539)

We now check for this header and corresponding logic. The WPT tests
mostly pass, but rely on the `contentDocument` of the iframe to be
`null`. This is not something we did before, which means that iframes
were able to access the contents of error pages.

Instead, we now mark the document as internal with an opaque origin
according to the spec [1]. We shouldn't do this post-fact, but is
required since we first need to construct the document and enter its
realm, before we determine that it is an invalid document.

Fixes #16103

[1]:
https://html.spec.whatwg.org/multipage/document-lifecycle.html#navigate-ua-inline

Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>

components/script/script_thread.rs

@@ -536,7 +536,7 @@ impl ScriptThread {
     pub(crate) fn page_headers_available(
         webview_id: WebViewId,
         pipeline_id: PipelineId,
-        metadata: Option<Metadata>,
+        metadata: Option<&Metadata>,
         cx: &mut js::context::JSContext,
     ) -> Option<DomRoot<ServoParser>> {
         with_script_thread(|script_thread| {
@@ -3088,7 +3088,7 @@ impl ScriptThread {
         &self,
         webview_id: WebViewId,
         pipeline_id: PipelineId,
-        metadata: Option<Metadata>,
+        metadata: Option<&Metadata>,
         cx: &mut js::context::JSContext,
     ) -> Option<DomRoot<ServoParser>> {
         if self.closed_pipelines.borrow().contains(&pipeline_id) {
@@ -3107,8 +3107,10 @@ impl ScriptThread {
 
         // https://html.spec.whatwg.org/multipage/#process-a-navigate-response
         // 2. If response's status is 204 or 205, then abort these steps.
+        //
+        // TODO: The specification has been updated and we no longer should abort.
         let is_204_205 = match metadata {
-            Some(ref metadata) => metadata.status.in_range(204..=205),
+            Some(metadata) => metadata.status.in_range(204..=205),
             _ => false,
         };
 
@@ -3345,7 +3347,7 @@ impl ScriptThread {
     /// objects, parses HTML and CSS, and kicks off initial layout.
     fn load(
         &self,
-        metadata: Metadata,
+        metadata: &Metadata,
         incomplete: InProgressLoad,
         cx: &mut js::context::JSContext,
     ) -> DomRoot<ServoParser> {
@@ -3489,6 +3491,13 @@ impl ScriptThread {
         }
         window.init_window_proxy(&window_proxy);
 
+        // https://html.spec.whatwg.org/multipage/#resource-metadata-management
+        // > The Document's source file's last modification date and time must be derived from
+        // > relevant features of the networking protocols used, e.g.
+        // > from the value of the HTTP `Last-Modified` header of the document,
+        // > or from metadata in the file system for local files.
+        // > If the last modification date and time are not known,
+        // > the attribute must return the current date and time in the above format.
         let last_modified = metadata.headers.as_ref().and_then(|headers| {
             headers.typed_get::<LastModified>().map(|tm| {
                 let tm: SystemTime = tm.into();
@@ -3504,6 +3513,7 @@ impl ScriptThread {
 
         let content_type: Option<Mime> = metadata
             .content_type
+            .clone()
             .map(Serde::into_inner)
             .map(Mime::from_ct);
         let encoding_hint_from_content_type = content_type