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(

components/script/dom/mod.rs

@@ -527,6 +527,7 @@ pub(crate) mod serviceworkercontainer;
 pub(crate) mod serviceworkerglobalscope;
 #[allow(dead_code)]
 pub(crate) mod serviceworkerregistration;
+pub(crate) mod servointernals;
 #[allow(dead_code)]
 pub(crate) mod servoparser;
 pub(crate) mod shadowroot;

components/script/dom/navigator.rs

@@ -27,6 +27,7 @@ use crate::dom::navigatorinfo;
 use crate::dom::permissions::Permissions;
 use crate::dom::pluginarray::PluginArray;
 use crate::dom::serviceworkercontainer::ServiceWorkerContainer;
+use crate::dom::servointernals::ServoInternals;
 #[cfg(feature = "webgpu")]
 use crate::dom::webgpu::gpu::GPU;
 use crate::dom::window::Window;
@@ -59,6 +60,7 @@ pub(crate) struct Navigator {
     gpu: MutNullableDom<GPU>,
     /// <https://www.w3.org/TR/gamepad/#dfn-hasgamepadgesture>
     has_gamepad_gesture: Cell<bool>,
+    servo_internals: MutNullableDom<ServoInternals>,
 }
 
 impl Navigator {
@@ -79,6 +81,7 @@ impl Navigator {
             #[cfg(feature = "webgpu")]
             gpu: Default::default(),
             has_gamepad_gesture: Cell::new(false),
+            servo_internals: Default::default(),
         }
     }
 
@@ -301,4 +304,10 @@ impl NavigatorMethods<crate::DomTypeHolder> for Navigator {
     fn HardwareConcurrency(&self) -> u64 {
         hardware_concurrency()
     }
+
+    /// <https://servo.org/internal-no-spec>
+    fn Servo(&self) -> DomRoot<ServoInternals> {
+        self.servo_internals
+            .or_init(|| ServoInternals::new(&self.global(), CanGc::note()))
+    }
 }

components/script/dom/servointernals.rs

@@ -0,0 +1,62 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use std::rc::Rc;
+
+use dom_struct::dom_struct;
+use profile_traits::mem::MemoryReportResult;
+use script_traits::ScriptMsg;
+
+use crate::dom::bindings::codegen::Bindings::ServoInternalsBinding::ServoInternalsMethods;
+use crate::dom::bindings::error::Error;
+use crate::dom::bindings::reflector::{DomGlobal, Reflector, reflect_dom_object};
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::globalscope::GlobalScope;
+use crate::dom::promise::Promise;
+use crate::realms::InRealm;
+use crate::routed_promise::{RoutedPromiseListener, route_promise};
+use crate::script_runtime::CanGc;
+
+#[dom_struct]
+pub(crate) struct ServoInternals {
+    reflector_: Reflector,
+}
+
+impl ServoInternals {
+    pub fn new_inherited() -> ServoInternals {
+        ServoInternals {
+            reflector_: Reflector::new(),
+        }
+    }
+
+    pub(crate) fn new(global: &GlobalScope, can_gc: CanGc) -> DomRoot<ServoInternals> {
+        reflect_dom_object(Box::new(ServoInternals::new_inherited()), global, can_gc)
+    }
+}
+
+impl ServoInternalsMethods<crate::DomTypeHolder> for ServoInternals {
+    /// <https://servo.org/internal-no-spec>
+    fn ReportMemory(&self, comp: InRealm, can_gc: CanGc) -> Rc<Promise> {
+        let global = &self.global();
+        let promise = Promise::new_in_current_realm(comp, can_gc);
+        let sender = route_promise(&promise, self);
+        let script_to_constellation_chan = global.script_to_constellation_chan();
+        if script_to_constellation_chan
+            .send(ScriptMsg::ReportMemory(sender))
+            .is_err()
+        {
+            promise.reject_error(Error::Operation, can_gc);
+        }
+        promise
+    }
+}
+
+impl RoutedPromiseListener for ServoInternals {
+    type Response = MemoryReportResult;
+
+    #[cfg_attr(crown, allow(crown::unrooted_must_root))]
+    fn handle_response(&self, response: Self::Response, promise: &Rc<Promise>, can_gc: CanGc) {
+        promise.resolve_native(&response.content, can_gc);
+    }
+}