Start reporting memory usage for Window and all nodes in all DOM trees for frame treese in script tasks.

components/script/mem.rs

@@ -0,0 +1,36 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+//! Routines for handling measuring the memory usage of arbitrary DOM nodes.
+
+use dom::bindings::codegen::InheritTypes::{DocumentCast, WindowCast, CharacterDataCast, NodeCast};
+use dom::eventtarget::{EventTarget, EventTargetTypeId};
+use dom::node::NodeTypeId;
+use libc;
+use util::mem::{HeapSizeOf, heap_size_of};
+
+// This is equivalent to measuring a Box<T>, except that DOM objects lose their
+// associated box in order to stash their pointers in a reserved slot of their
+// JS reflector. It is assumed that the caller passes a pointer to the most-derived
+// type that this pointer represents, or the actual heap usage of the pointee will
+// be under-reported.
+fn heap_size_of_self_and_children<T: HeapSizeOf>(obj: &T) -> usize {
+    heap_size_of(obj as *const T as *const libc::c_void) + obj.heap_size_of_children()
+}
+
+pub fn heap_size_of_eventtarget(target: &EventTarget) -> usize {
+    //TODO: add more specific matches for concrete element types as derive(HeapSizeOf) is
+    //      added to each one.
+    match target.type_id() {
+        &EventTargetTypeId::Window =>
+            heap_size_of_self_and_children(WindowCast::to_ref(target).unwrap()),
+        &EventTargetTypeId::Node(NodeTypeId::CharacterData(_)) =>
+            heap_size_of_self_and_children(CharacterDataCast::to_ref(target).unwrap()),
+        &EventTargetTypeId::Node(NodeTypeId::Document) =>
+            heap_size_of_self_and_children(DocumentCast::to_ref(target).unwrap()),
+        &EventTargetTypeId::Node(_) =>
+            heap_size_of_self_and_children(NodeCast::to_ref(target).unwrap()),
+        _ => 0,
+    }
+}