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/style/invalidation/element/invalidation_map.rs

@@ -55,14 +55,12 @@ pub fn dir_selector_to_state(s: &[u16]) -> ElementState {
 /// This allows us to quickly scan through the dependency sites of all style
 /// rules and determine the maximum effect that a given state or attribute
 /// change may have on the style of elements in the document.
-#[derive(Clone, Debug)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Clone, Debug, MallocSizeOf)]
 pub struct Dependency {
     /// The dependency selector.
     #[cfg_attr(feature = "gecko",
                ignore_malloc_size_of = "CssRules have primary refs, we measure there")]
-    #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
+    #[cfg_attr(feature = "servo", ignore_malloc_size_of = "Arc")]
     pub selector: Selector<SelectorImpl>,
 
     /// The offset into the selector that we should match on.
@@ -115,9 +113,7 @@ impl SelectorMapEntry for Dependency {
 
 /// The same, but for state selectors, which can track more exactly what state
 /// do they track.
-#[derive(Clone, Debug)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Clone, Debug, MallocSizeOf)]
 pub struct StateDependency {
     /// The other dependency fields.
     pub dep: Dependency,
@@ -139,9 +135,7 @@ impl SelectorMapEntry for StateDependency {
 /// In particular, we want to lookup as few things as possible to get the fewer
 /// selectors the better, so this looks up by id, class, or looks at the list of
 /// state/other attribute affecting selectors.
-#[derive(Debug)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Debug, MallocSizeOf)]
 pub struct InvalidationMap {
     /// A map from a given class name to all the selectors with that class
     /// selector.