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/stylesheets/keyframes_rule.rs

@@ -96,9 +96,7 @@ impl DeepCloneWithLock for KeyframesRule {
 
 /// A number from 0 to 1, indicating the percentage of the animation when this
 /// keyframe should run.
-#[derive(Clone, Copy, Debug, PartialEq, PartialOrd)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, PartialOrd)]
 pub struct KeyframePercentage(pub f32);
 
 impl ::std::cmp::Ord for KeyframePercentage {
@@ -260,16 +258,14 @@ impl DeepCloneWithLock for Keyframe {
 /// declarations to apply.
 ///
 /// TODO: Find a better name for this?
-#[derive(Debug)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Debug, MallocSizeOf)]
 pub enum KeyframesStepValue {
     /// A step formed by a declaration block specified by the CSS.
     Declarations {
         /// The declaration block per se.
         #[cfg_attr(feature = "gecko",
                    ignore_malloc_size_of = "XXX: Primary ref, measure if DMD says it's worthwhile")]
-        #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
+        #[cfg_attr(feature = "servo", ignore_malloc_size_of = "Arc")]
         block: Arc<Locked<PropertyDeclarationBlock>>
     },
     /// A synthetic step computed from the current computed values at the time
@@ -278,9 +274,7 @@ pub enum KeyframesStepValue {
 }
 
 /// A single step from a keyframe animation.
-#[derive(Debug)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Debug, MallocSizeOf)]
 pub struct KeyframesStep {
     /// The percentage of the animation duration when this step starts.
     pub start_percentage: KeyframePercentage,
@@ -350,9 +344,7 @@ impl KeyframesStep {
 /// of keyframes, in order.
 ///
 /// It only takes into account animable properties.
-#[derive(Debug)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Debug, MallocSizeOf)]
 pub struct KeyframesAnimation {
     /// The difference steps of the animation.
     pub steps: Vec<KeyframesStep>,