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/webgl_extensions/extensions.rs

@@ -13,9 +13,9 @@ use dom::bindings::trace::JSTraceable;
 use dom::webglrenderingcontext::WebGLRenderingContext;
 use fnv::{FnvHashMap, FnvHashSet};
 use gleam::gl::GLenum;
-use heapsize::HeapSizeOf;
 use js::jsapi::JSContext;
 use js::jsval::JSVal;
+use malloc_size_of::MallocSizeOf;
 use ref_filter_map::ref_filter_map;
 use std::cell::Ref;
 use std::collections::HashMap;
@@ -45,7 +45,7 @@ const DEFAULT_DISABLED_GET_PARAMETER_NAMES: [GLenum; 1] = [
 ];
 
 /// WebGL features that are enabled/disabled by WebGL Extensions.
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 struct WebGLExtensionFeatures {
     gl_extensions: FnvHashSet<String>,
     disabled_tex_types: FnvHashSet<GLenum>,
@@ -74,7 +74,7 @@ impl Default for WebGLExtensionFeatures {
 
 /// Handles the list of implemented, supported and enabled WebGL extensions.
 #[must_root]
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 pub struct WebGLExtensions {
     extensions: DomRefCell<HashMap<String, Box<WebGLExtensionWrapper>>>,
     features: DomRefCell<WebGLExtensionFeatures>,
@@ -97,7 +97,7 @@ impl WebGLExtensions {
         }
     }
 
-    pub fn register<T:'static + WebGLExtension + JSTraceable + HeapSizeOf>(&self) {
+    pub fn register<T:'static + WebGLExtension + JSTraceable + MallocSizeOf>(&self) {
         let name = T::name().to_uppercase();
         self.extensions.borrow_mut().insert(name, Box::new(TypedWebGLExtensionWrapper::<T>::new()));
     }
@@ -122,7 +122,7 @@ impl WebGLExtensions {
 
     pub fn is_enabled<T>(&self) -> bool
     where
-        T: 'static + WebGLExtension + JSTraceable + HeapSizeOf
+        T: 'static + WebGLExtension + JSTraceable + MallocSizeOf
     {
         let name = T::name().to_uppercase();
         self.extensions.borrow().get(&name).map_or(false, |ext| { ext.is_enabled() })
@@ -130,7 +130,7 @@ impl WebGLExtensions {
 
     pub fn get_dom_object<T>(&self) -> Option<DomRoot<T::Extension>>
     where
-        T: 'static + WebGLExtension + JSTraceable + HeapSizeOf
+        T: 'static + WebGLExtension + JSTraceable + MallocSizeOf
     {
         let name = T::name().to_uppercase();
         self.extensions.borrow().get(&name).and_then(|extension| {
@@ -224,15 +224,15 @@ impl WebGLExtensions {
 }
 
 // Helper structs
-#[derive(Eq, Hash, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Eq, Hash, JSTraceable, MallocSizeOf, PartialEq)]
 struct TexFormatType(u32, u32);
 
 type WebGLQueryParameterFunc = Fn(*mut JSContext, &WebGLRenderingContext)
                                -> Result<JSVal, WebGLError>;
 
-#[derive(HeapSizeOf)]
+#[derive(MallocSizeOf)]
 struct WebGLQueryParameterHandler {
-    #[ignore_heap_size_of = "Closures are hard"]
+    #[ignore_malloc_size_of = "Closures are hard"]
     func: Box<WebGLQueryParameterFunc>
 }