Various memory measurement improvements (#36834)

The two significant changes here are 1) a commit that frees memory used
to perform memory reporting once the reporting is complete, 2) memory
reporting for the system font service. There are various other commits
that remove `#[ignore_malloc_size_of]` attributes for data that we are
now able to measure, but they do not significantly change our
measurements when testing servo.org.

Testing: Comparing the output of about:memory on servo.org.

---------

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

components/script/dom/bindings/cell.rs

@@ -10,6 +10,7 @@ pub(crate) use std::cell::{Ref, RefCell, RefMut};
 
 #[cfg(feature = "refcell_backtrace")]
 pub(crate) use accountable_refcell::{Ref, RefCell, RefMut, ref_filter_map};
+use malloc_size_of::{MallocConditionalSizeOf, MallocSizeOfOps};
 #[cfg(not(feature = "refcell_backtrace"))]
 pub(crate) use ref_filter_map::ref_filter_map;
 
@@ -24,6 +25,12 @@ pub(crate) struct DomRefCell<T> {
     value: RefCell<T>,
 }
 
+impl<T: MallocConditionalSizeOf> MallocConditionalSizeOf for DomRefCell<T> {
+    fn conditional_size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        self.value.borrow().conditional_size_of(ops)
+    }
+}
+
 // Functionality specific to Servo's `DomRefCell` type
 // ===================================================
 

components/script/dom/element.rs

@@ -179,7 +179,7 @@ pub struct Element {
     /// <https://dom.spec.whatwg.org/#concept-element-is-value>
     #[no_trace]
     is: DomRefCell<Option<LocalName>>,
-    #[ignore_malloc_size_of = "Arc"]
+    #[conditional_malloc_size_of]
     #[no_trace]
     style_attribute: DomRefCell<Option<Arc<Locked<PropertyDeclarationBlock>>>>,
     attr_list: MutNullableDom<NamedNodeMap>,

components/script/dom/htmlimageelement.rs

@@ -97,6 +97,7 @@ enum ParseState {
     AfterDescriptor,
 }
 
+#[derive(MallocSizeOf)]
 pub(crate) struct SourceSet {
     image_sources: Vec<ImageSource>,
     source_size: SourceSizeList,
@@ -111,13 +112,13 @@ impl SourceSet {
     }
 }
 
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
 pub struct ImageSource {
     pub url: String,
     pub descriptor: Descriptor,
 }
 
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
 pub struct Descriptor {
     pub width: Option<u32>,
     pub density: Option<f64>,
@@ -145,7 +146,7 @@ struct ImageRequest {
     parsed_url: Option<ServoUrl>,
     source_url: Option<USVString>,
     blocker: DomRefCell<Option<LoadBlocker>>,
-    #[ignore_malloc_size_of = "Arc"]
+    #[conditional_malloc_size_of]
     #[no_trace]
     image: Option<Arc<Image>>,
     #[no_trace]
@@ -162,7 +163,6 @@ pub(crate) struct HTMLImageElement {
     pending_request: DomRefCell<ImageRequest>,
     form_owner: MutNullableDom<HTMLFormElement>,
     generation: Cell<u32>,
-    #[ignore_malloc_size_of = "SourceSet"]
     source_set: DomRefCell<SourceSet>,
     last_selected_source: DomRefCell<Option<USVString>>,
     #[ignore_malloc_size_of = "promises are hard"]

components/script/dom/htmllinkelement.rs

@@ -98,7 +98,7 @@ pub(crate) struct HTMLLinkElement {
     #[no_trace]
     relations: Cell<LinkRelations>,
 
-    #[ignore_malloc_size_of = "Arc"]
+    #[conditional_malloc_size_of]
     #[no_trace]
     stylesheet: DomRefCell<Option<Arc<Stylesheet>>>,
     cssom_stylesheet: MutNullableDom<CSSStyleSheet>,

components/script/dom/htmlscriptelement.rs

@@ -281,19 +281,18 @@ pub(crate) enum ScriptType {
 pub(crate) struct CompiledSourceCode {
     #[ignore_malloc_size_of = "SM handles JS values"]
     pub(crate) source_code: Stencil,
-    #[ignore_malloc_size_of = "Rc is hard"]
+    #[conditional_malloc_size_of = "Rc is hard"]
     pub(crate) original_text: Rc<DOMString>,
 }
 
-#[derive(JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 pub(crate) enum SourceCode {
-    Text(Rc<DOMString>),
+    Text(#[conditional_malloc_size_of] Rc<DOMString>),
     Compiled(CompiledSourceCode),
 }
 
 #[derive(JSTraceable, MallocSizeOf)]
 pub(crate) struct ScriptOrigin {
-    #[ignore_malloc_size_of = "Rc is hard"]
     code: SourceCode,
     #[no_trace]
     url: ServoUrl,

components/script/dom/htmlstyleelement.rs

@@ -34,7 +34,7 @@ use crate::stylesheet_loader::{StylesheetLoader, StylesheetOwner};
 #[dom_struct]
 pub(crate) struct HTMLStyleElement {
     htmlelement: HTMLElement,
-    #[ignore_malloc_size_of = "Arc"]
+    #[conditional_malloc_size_of]
     #[no_trace]
     stylesheet: DomRefCell<Option<Arc<Stylesheet>>>,
     cssom_stylesheet: MutNullableDom<CSSStyleSheet>,