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/canvas_traits/canvas.rs

@@ -82,13 +82,13 @@ pub enum FromScriptMsg {
     SendPixels(IpcSender<Option<Vec<u8>>>),
 }
 
-#[derive(Clone, Deserialize, HeapSizeOf, Serialize)]
+#[derive(Clone, Deserialize, MallocSizeOf, Serialize)]
 pub struct CanvasGradientStop {
     pub offset: f64,
     pub color: RGBA,
 }
 
-#[derive(Clone, Deserialize, HeapSizeOf, Serialize)]
+#[derive(Clone, Deserialize, MallocSizeOf, Serialize)]
 pub struct LinearGradientStyle {
     pub x0: f64,
     pub y0: f64,
@@ -110,7 +110,7 @@ impl LinearGradientStyle {
     }
 }
 
-#[derive(Clone, Deserialize, HeapSizeOf, Serialize)]
+#[derive(Clone, Deserialize, MallocSizeOf, Serialize)]
 pub struct RadialGradientStyle {
     pub x0: f64,
     pub y0: f64,
@@ -165,7 +165,7 @@ pub enum FillOrStrokeStyle {
     Surface(SurfaceStyle),
 }
 
-#[derive(Clone, Copy, Deserialize, HeapSizeOf, PartialEq, Serialize)]
+#[derive(Clone, Copy, Deserialize, MallocSizeOf, PartialEq, Serialize)]
 pub enum LineCapStyle {
     Butt = 0,
     Round = 1,
@@ -185,7 +185,7 @@ impl FromStr for LineCapStyle {
     }
 }
 
-#[derive(Clone, Copy, Deserialize, HeapSizeOf, PartialEq, Serialize)]
+#[derive(Clone, Copy, Deserialize, MallocSizeOf, PartialEq, Serialize)]
 pub enum LineJoinStyle {
     Round = 0,
     Bevel = 1,
@@ -227,7 +227,7 @@ impl FromStr for RepetitionStyle {
     }
 }
 
-#[derive(Clone, Copy, Deserialize, HeapSizeOf, PartialEq, Serialize)]
+#[derive(Clone, Copy, Deserialize, MallocSizeOf, PartialEq, Serialize)]
 pub enum CompositionStyle {
     SrcIn,
     SrcOut,
@@ -281,7 +281,7 @@ impl CompositionStyle {
     }
 }
 
-#[derive(Clone, Copy, Deserialize, HeapSizeOf, PartialEq, Serialize)]
+#[derive(Clone, Copy, Deserialize, MallocSizeOf, PartialEq, Serialize)]
 pub enum BlendingStyle {
     Multiply,
     Screen,
@@ -347,7 +347,7 @@ impl BlendingStyle {
     }
 }
 
-#[derive(Clone, Copy, Deserialize, HeapSizeOf, PartialEq, Serialize)]
+#[derive(Clone, Copy, Deserialize, MallocSizeOf, PartialEq, Serialize)]
 pub enum CompositionOrBlending {
     Composition(CompositionStyle),
     Blending(BlendingStyle),