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/script_thread.rs

@@ -73,7 +73,8 @@ use js::jsapi::{JSAutoCompartment, JSContext, JS_SetWrapObjectCallbacks};
 use js::jsapi::{JSTracer, SetWindowProxyClass};
 use js::jsval::UndefinedValue;
 use js::rust::Runtime;
-use mem::heap_size_of_self_and_children;
+use malloc_size_of::{malloc_size_of, MallocSizeOfOps};
+use mem::malloc_size_of_including_self;
 use metrics::PaintTimeMetrics;
 use microtask::{MicrotaskQueue, Microtask};
 use msg::constellation_msg::{BrowsingContextId, FrameType, PipelineId, PipelineNamespace, TopLevelBrowsingContextId};
@@ -1503,14 +1504,17 @@ impl ScriptThread {
         let mut path_seg = String::from("url(");
         let mut dom_tree_size = 0;
         let mut reports = vec![];
+        // Servo uses vanilla jemalloc, which doesn't have a
+        // malloc_enclosing_size_of function.
+        let mut ops = MallocSizeOfOps::new(malloc_size_of, None, None);
 
         for (_, document) in self.documents.borrow().iter() {
             let current_url = document.url();
 
             for child in document.upcast::<Node>().traverse_preorder() {
-                dom_tree_size += heap_size_of_self_and_children(&*child);
+                dom_tree_size += malloc_size_of_including_self(&mut ops, &*child);
             }
-            dom_tree_size += heap_size_of_self_and_children(document.window());
+            dom_tree_size += malloc_size_of_including_self(&mut ops, document.window());
 
             if reports.len() > 0 {
                 path_seg.push_str(", ");