Replace all uses of the heapsize crate with malloc_size_of.

Servo currently uses `heapsize`, but Stylo/Gecko use `malloc_size_of`.
`malloc_size_of` is better -- it handles various cases that `heapsize` does not
-- so this patch changes Servo to use `malloc_size_of`.

This patch makes the following changes to the `malloc_size_of` crate.

- Adds `MallocSizeOf` trait implementations for numerous types, some built-in
  (e.g. `VecDeque`), some external and Servo-only (e.g. `string_cache`).

- Makes `enclosing_size_of_op` optional, because vanilla jemalloc doesn't
  support that operation.

- For `HashSet`/`HashMap`, falls back to a computed estimate when
  `enclosing_size_of_op` isn't available.

- Adds an extern "C" `malloc_size_of` function that does the actual heap
  measurement; this is based on the same functions from the `heapsize` crate.

This patch makes the following changes elsewhere.

- Converts all the uses of `heapsize` to instead use `malloc_size_of`.

- Disables the "heapsize"/"heap_size" feature for the external crates that
  provide it.

- Removes the `HeapSizeOf` implementation from `hashglobe`.

- Adds `ignore` annotations to a few `Rc`/`Arc`, because `malloc_size_of`
  doesn't derive those types, unlike `heapsize`.

components/script/dom/element.rs

@@ -140,7 +140,7 @@ pub struct Element {
     attrs: DomRefCell<Vec<Dom<Attr>>>,
     id_attribute: DomRefCell<Option<Atom>>,
     is: DomRefCell<Option<LocalName>>,
-    #[ignore_heap_size_of = "Arc"]
+    #[ignore_malloc_size_of = "Arc"]
     style_attribute: DomRefCell<Option<Arc<Locked<PropertyDeclarationBlock>>>>,
     attr_list: MutNullableDom<NamedNodeMap>,
     class_list: MutNullableDom<DOMTokenList>,
@@ -149,12 +149,12 @@ pub struct Element {
     /// operations may require restyling this element or its descendants. The
     /// flags are not atomic, so the style system takes care of only set them
     /// when it has exclusive access to the element.
-    #[ignore_heap_size_of = "bitflags defined in rust-selectors"]
+    #[ignore_malloc_size_of = "bitflags defined in rust-selectors"]
     selector_flags: Cell<ElementSelectorFlags>,
     /// <https://html.spec.whatwg.org/multipage/#custom-element-reaction-queue>
     custom_element_reaction_queue: DomRefCell<Vec<CustomElementReaction>>,
     /// <https://dom.spec.whatwg.org/#concept-element-custom-element-definition>
-    #[ignore_heap_size_of = "Rc"]
+    #[ignore_malloc_size_of = "Rc"]
     custom_element_definition: DomRefCell<Option<Rc<CustomElementDefinition>>>,
     /// <https://dom.spec.whatwg.org/#concept-element-custom-element-state>
     custom_element_state: Cell<CustomElementState>,
@@ -176,7 +176,7 @@ impl fmt::Debug for DomRoot<Element> {
     }
 }
 
-#[derive(HeapSizeOf, PartialEq)]
+#[derive(MallocSizeOf, PartialEq)]
 pub enum ElementCreator {
     ParserCreated(u64),
     ScriptCreated,
@@ -188,7 +188,7 @@ pub enum CustomElementCreationMode {
 }
 
 /// <https://dom.spec.whatwg.org/#concept-element-custom-element-state>
-#[derive(Clone, Copy, Eq, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Clone, Copy, Eq, JSTraceable, MallocSizeOf, PartialEq)]
 pub enum CustomElementState {
     Undefined,
     Failed,
@@ -3025,7 +3025,7 @@ impl<'a> AttributeMutation<'a> {
 /// A holder for an element's "tag name", which will be lazily
 /// resolved and cached. Should be reset when the document
 /// owner changes.
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 struct TagName {
     ptr: DomRefCell<Option<LocalName>>,
 }