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/eventtarget.rs

@@ -32,7 +32,6 @@ use dom::virtualmethods::VirtualMethods;
 use dom::window::Window;
 use dom_struct::dom_struct;
 use fnv::FnvHasher;
-use heapsize::HeapSizeOf;
 use js::jsapi::{CompileFunction, JS_GetFunctionObject, JSAutoCompartment};
 use js::rust::{AutoObjectVectorWrapper, CompileOptionsWrapper};
 use libc::{c_char, size_t};
@@ -48,11 +47,19 @@ use std::ops::{Deref, DerefMut};
 use std::ptr;
 use std::rc::Rc;
 
-#[derive(Clone, JSTraceable, PartialEq)]
+#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
 pub enum CommonEventHandler {
-    EventHandler(Rc<EventHandlerNonNull>),
-    ErrorEventHandler(Rc<OnErrorEventHandlerNonNull>),
-    BeforeUnloadEventHandler(Rc<OnBeforeUnloadEventHandlerNonNull>),
+    EventHandler(
+        #[ignore_malloc_size_of = "Rc"]
+        Rc<EventHandlerNonNull>),
+
+    ErrorEventHandler(
+        #[ignore_malloc_size_of = "Rc"]
+        Rc<OnErrorEventHandlerNonNull>),
+
+    BeforeUnloadEventHandler(
+        #[ignore_malloc_size_of = "Rc"]
+        Rc<OnBeforeUnloadEventHandlerNonNull>),
 }
 
 impl CommonEventHandler {
@@ -65,14 +72,14 @@ impl CommonEventHandler {
     }
 }
 
-#[derive(Clone, Copy, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Clone, Copy, JSTraceable, MallocSizeOf, PartialEq)]
 pub enum ListenerPhase {
     Capturing,
     Bubbling,
 }
 
 /// <https://html.spec.whatwg.org/multipage/#internal-raw-uncompiled-handler>
-#[derive(Clone, JSTraceable, PartialEq)]
+#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
 struct InternalRawUncompiledHandler {
     source: DOMString,
     url: ServoUrl,
@@ -80,7 +87,7 @@ struct InternalRawUncompiledHandler {
 }
 
 /// A representation of an event handler, either compiled or uncompiled raw source, or null.
-#[derive(Clone, JSTraceable, PartialEq)]
+#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
 enum InlineEventListener {
     Uncompiled(InternalRawUncompiledHandler),
     Compiled(CommonEventHandler),
@@ -110,19 +117,12 @@ impl InlineEventListener {
     }
 }
 
-#[derive(Clone, JSTraceable, PartialEq)]
+#[derive(Clone, JSTraceable, MallocSizeOf, PartialEq)]
 enum EventListenerType {
-    Additive(Rc<EventListener>),
+    Additive(#[ignore_malloc_size_of = "Rc"] Rc<EventListener>),
     Inline(InlineEventListener),
 }
 
-impl HeapSizeOf for EventListenerType {
-    fn heap_size_of_children(&self) -> usize {
-        // FIXME: Rc<T> isn't HeapSizeOf and we can't ignore it due to #6870 and #6871
-        0
-    }
-}
-
 impl EventListenerType {
     fn get_compiled_listener(&mut self, owner: &EventTarget, ty: &Atom)
                              -> Option<CompiledEventListener> {
@@ -225,14 +225,14 @@ impl CompiledEventListener {
     }
 }
 
-#[derive(Clone, DenyPublicFields, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Clone, DenyPublicFields, JSTraceable, MallocSizeOf, PartialEq)]
 /// A listener in a collection of event listeners.
 struct EventListenerEntry {
     phase: ListenerPhase,
     listener: EventListenerType
 }
 
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 /// A mix of potentially uncompiled and compiled event listeners of the same type.
 struct EventListeners(Vec<EventListenerEntry>);