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/range.rs

@@ -27,8 +27,8 @@ use dom::node::{Node, UnbindContext};
 use dom::text::Text;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use heapsize::HeapSizeOf;
 use js::jsapi::JSTracer;
+use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use std::cell::{Cell, UnsafeCell};
 use std::cmp::{Ord, Ordering, PartialEq, PartialOrd};
 
@@ -933,7 +933,7 @@ impl RangeMethods for Range {
     }
 }
 
-#[derive(DenyPublicFields, HeapSizeOf, JSTraceable)]
+#[derive(DenyPublicFields, JSTraceable, MallocSizeOf)]
 #[must_root]
 pub struct BoundaryPoint {
     node: MutDom<Node>,
@@ -1251,9 +1251,9 @@ impl WeakRangeVec {
 }
 
 #[allow(unsafe_code)]
-impl HeapSizeOf for WeakRangeVec {
-    fn heap_size_of_children(&self) -> usize {
-        unsafe { (*self.cell.get()).heap_size_of_children() }
+impl MallocSizeOf for WeakRangeVec {
+    fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        unsafe { (*self.cell.get()).size_of(ops) }
     }
 }