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/bindings/weakref.rs

@@ -14,10 +14,10 @@
 use dom::bindings::reflector::DomObject;
 use dom::bindings::root::DomRoot;
 use dom::bindings::trace::JSTraceable;
-use heapsize::HeapSizeOf;
 use js::jsapi::{JSTracer, JS_GetReservedSlot, JS_SetReservedSlot};
 use js::jsval::PrivateValue;
 use libc::c_void;
+use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use nonzero::NonZero;
 use std::cell::{Cell, UnsafeCell};
 use std::mem;
@@ -110,8 +110,8 @@ impl<T: WeakReferenceable> Clone for WeakRef<T> {
     }
 }
 
-impl<T: WeakReferenceable> HeapSizeOf for WeakRef<T> {
-    fn heap_size_of_children(&self) -> usize {
+impl<T: WeakReferenceable> MallocSizeOf for WeakRef<T> {
+    fn size_of(&self, _ops: &mut MallocSizeOfOps) -> usize {
         0
     }
 }
@@ -188,8 +188,8 @@ impl<T: WeakReferenceable> MutableWeakRef<T> {
     }
 }
 
-impl<T: WeakReferenceable> HeapSizeOf for MutableWeakRef<T> {
-    fn heap_size_of_children(&self) -> usize {
+impl<T: WeakReferenceable> MallocSizeOf for MutableWeakRef<T> {
+    fn size_of(&self, _ops: &mut MallocSizeOfOps) -> usize {
         0
     }
 }
@@ -210,7 +210,7 @@ unsafe impl<T: WeakReferenceable> JSTraceable for MutableWeakRef<T> {
 /// A vector of weak references. On tracing, the vector retains
 /// only references which still point to live objects.
 #[allow_unrooted_interior]
-#[derive(HeapSizeOf)]
+#[derive(MallocSizeOf)]
 pub struct WeakRefVec<T: WeakReferenceable> {
     vec: Vec<WeakRef<T>>,
 }