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/servoparser/mod.rs

@@ -74,13 +74,13 @@ pub struct ServoParser {
     /// The document associated with this parser.
     document: Dom<Document>,
     /// Input received from network.
-    #[ignore_heap_size_of = "Defined in html5ever"]
+    #[ignore_malloc_size_of = "Defined in html5ever"]
     network_input: DomRefCell<BufferQueue>,
     /// Part of an UTF-8 code point spanning input chunks
-    #[ignore_heap_size_of = "Defined in html5ever"]
+    #[ignore_malloc_size_of = "Defined in html5ever"]
     incomplete_utf8: DomRefCell<Option<IncompleteUtf8>>,
     /// Input received from script. Used only to support document.write().
-    #[ignore_heap_size_of = "Defined in html5ever"]
+    #[ignore_malloc_size_of = "Defined in html5ever"]
     script_input: DomRefCell<BufferQueue>,
     /// The tokenizer of this parser.
     tokenizer: DomRefCell<Tokenizer>,
@@ -493,13 +493,13 @@ impl<I> Iterator for FragmentParsingResult<I>
     }
 }
 
-#[derive(HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(JSTraceable, MallocSizeOf, PartialEq)]
 enum ParserKind {
     Normal,
     ScriptCreated,
 }
 
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 #[must_root]
 enum Tokenizer {
     Html(self::html::Tokenizer),
@@ -742,7 +742,7 @@ fn insert(parent: &Node, reference_child: Option<&Node>, child: NodeOrText<Dom<N
     }
 }
 
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 #[must_root]
 pub struct Sink {
     base_url: ServoUrl,