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/url/origin.rs

@@ -11,7 +11,7 @@ use url_serde;
 use uuid::Uuid;
 
 /// The origin of an URL
-#[derive(Clone, Debug, Deserialize, Eq, HeapSizeOf, PartialEq, Serialize)]
+#[derive(Clone, Debug, Deserialize, Eq, MallocSizeOf, PartialEq, Serialize)]
 pub enum ImmutableOrigin {
     /// A globally unique identifier
     Opaque(OpaqueOrigin),
@@ -98,13 +98,13 @@ impl ImmutableOrigin {
 #[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize)]
 pub struct OpaqueOrigin(Uuid);
 
-known_heap_size!(0, OpaqueOrigin);
+malloc_size_of_is_0!(OpaqueOrigin);
 
 /// A representation of an [origin](https://html.spec.whatwg.org/multipage/#origin-2).
 #[derive(Clone, Debug)]
 pub struct MutableOrigin(Rc<(ImmutableOrigin, RefCell<Option<Host>>)>);
 
-known_heap_size!(0, MutableOrigin);
+malloc_size_of_is_0!(MutableOrigin);
 
 impl MutableOrigin {
     pub fn new(origin: ImmutableOrigin) -> MutableOrigin {