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/values/generics/border.rs

@@ -10,9 +10,7 @@ use values::generics::rect::Rect;
 use values::generics::size::Size;
 
 /// A generic value for a single side of a `border-image-width` property.
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
 pub enum BorderImageSideWidth<LengthOrPercentage, Number> {
     /// `<length-or-percentage>`
     Length(LengthOrPercentage),
@@ -23,9 +21,7 @@ pub enum BorderImageSideWidth<LengthOrPercentage, Number> {
 }
 
 /// A generic value for the `border-image-slice` property.
-#[derive(Clone, Copy, Debug, PartialEq, ToComputedValue)]
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
 pub struct BorderImageSlice<NumberOrPercentage> {
     /// The offsets.
     pub offsets: Rect<NumberOrPercentage>,
@@ -34,10 +30,8 @@ pub struct BorderImageSlice<NumberOrPercentage> {
 }
 
 /// A generic value for the `border-*-radius` longhand properties.
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 #[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug)]
-#[derive(PartialEq, ToComputedValue, ToCss)]
+#[derive(MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
 pub struct BorderCornerRadius<L>(pub Size<L>);
 
 impl<L> BorderCornerRadius<L> {
@@ -48,9 +42,7 @@ impl<L> BorderCornerRadius<L> {
 }
 
 /// A generic value for the `border-spacing` property.
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf)]
 #[derive(PartialEq, ToAnimatedValue, ToComputedValue, ToCss)]
 pub struct BorderSpacing<L>(pub Size<L>);
 
@@ -64,10 +56,8 @@ impl<L> BorderSpacing<L> {
 /// A generic value for `border-radius`, `outline-radius` and `inset()`.
 ///
 /// <https://drafts.csswg.org/css-backgrounds-3/#border-radius>
-#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 #[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug)]
-#[derive(PartialEq, ToComputedValue)]
+#[derive(MallocSizeOf, PartialEq, ToComputedValue)]
 pub struct BorderRadius<LengthOrPercentage> {
     /// The top left radius.
     pub top_left: BorderCornerRadius<LengthOrPercentage>,