Add an about:memory page (#35728)

This patch exposes a servo internal DOM API that is only made available to about:
pages on the navigator object to request memory reports. The about:memory page itself is
loaded like other html resources (eg. bad cert, net error) and makes use of this new API.

On the implementation side, notable changes:
- components/script/routed_promise.rs abstracts the setup used to fulfill a promise when the
  work needs to be routed through the constellation. The goal is to migrate other similar
  promise APIs in followup (eg. dom/webgpu/gpu.rs, bluetooth.rs).
- a new message is added to request a report from the memory reporter, and the memory reporter
  creates a json representation of the set of memory reports.
- the post-processing of memory reports is done in Javascript in the about-memory.html page,
  providing the same results as the current Rust code that outputs to stdout. We can decide
  later if we want to remove the current output.

Signed-off-by: webbeef <me@webbeef.org>

components/script/dom/bindings/interface.rs

@@ -43,6 +43,8 @@ use crate::dom::bindings::principals::ServoJSPrincipals;
 use crate::dom::bindings::utils::{
     DOM_PROTOTYPE_SLOT, DOMJSClass, JSCLASS_DOM_GLOBAL, ProtoOrIfaceArray, get_proto_or_iface_array,
 };
+use crate::dom::globalscope::GlobalScope;
+use crate::realms::{AlreadyInRealm, InRealm};
 use crate::script_runtime::JSContext as SafeJSContext;
 
 /// The class of a non-callback interface object.
@@ -423,6 +425,16 @@ pub(crate) fn is_exposed_in(object: HandleObject, globals: Globals) -> bool {
     }
 }
 
+/// The navigator.servo api is only exposed to about: pages except about:blank
+pub(crate) fn is_servo_internal(cx: SafeJSContext, _object: HandleObject) -> bool {
+    unsafe {
+        let in_realm_proof = AlreadyInRealm::assert_for_cx(cx);
+        let global_scope = GlobalScope::from_context(*cx, InRealm::Already(&in_realm_proof));
+        let url = global_scope.get_url();
+        url.scheme() == "about" && url.as_str() != "about:blank"
+    }
+}
+
 /// Define a property with a given name on the global object. Should be called
 /// through the resolve hook.
 pub(crate) fn define_on_global_object(