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/hashglobe/src/fake.rs

@@ -14,7 +14,6 @@
 //! These methods are a lie. They are not actually fallible. This is just to make
 //! it smooth to switch between hashmap impls in a codebase.
 
-use heapsize::HeapSizeOf;
 use std::collections::HashMap as StdMap;
 use std::collections::HashSet as StdSet;
 use std::fmt;
@@ -161,14 +160,6 @@ impl<T, S> HashSet<T, S>
 // Pass through trait impls
 // We can't derive these since the bounds are not obvious to the derive macro
 
-
-impl<K: HeapSizeOf + Hash + Eq, V: HeapSizeOf, S: BuildHasher>
-        HeapSizeOf for HashMap<K, V, S> {
-    fn heap_size_of_children(&self) -> usize {
-        self.0.heap_size_of_children()
-    }
-}
-
 impl<K: Hash + Eq, V, S: BuildHasher + Default> Default for HashMap<K, V, S> {
     fn default() -> Self {
         HashMap(Default::default())
@@ -225,13 +216,6 @@ impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S>
     }
 }
 
-
-impl<T: HeapSizeOf + Eq + Hash, S: BuildHasher> HeapSizeOf for HashSet<T, S> {
-    fn heap_size_of_children(&self) -> usize {
-        self.0.heap_size_of_children()
-    }
-}
-
 impl<T: Eq + Hash, S: BuildHasher + Default> Default for HashSet<T, S> {
     fn default() -> Self {
         HashSet(Default::default())

components/hashglobe/src/lib.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-extern crate heapsize;
-
 pub mod alloc;
 pub mod diagnostic;
 pub mod hash_map;