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/filereader.rs

@@ -39,7 +39,7 @@ use task::TaskCanceller;
 use task_source::TaskSource;
 use task_source::file_reading::{FileReadingTask, FileReadingTaskSource};
 
-#[derive(Clone, Copy, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Clone, Copy, JSTraceable, MallocSizeOf, PartialEq)]
 pub enum FileReaderFunction {
     ReadAsText,
     ReadAsDataUrl,
@@ -48,7 +48,7 @@ pub enum FileReaderFunction {
 
 pub type TrustedFileReader = Trusted<FileReader>;
 
-#[derive(Clone, HeapSizeOf)]
+#[derive(Clone, MallocSizeOf)]
 pub struct ReadMetaData {
     pub blobtype: String,
     pub label: Option<String>,
@@ -66,18 +66,18 @@ impl ReadMetaData {
     }
 }
 
-#[derive(Clone, Copy, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Clone, Copy, JSTraceable, MallocSizeOf, PartialEq)]
 pub struct GenerationId(u32);
 
 #[repr(u16)]
-#[derive(Clone, Copy, Debug, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Clone, Copy, Debug, JSTraceable, MallocSizeOf, PartialEq)]
 pub enum FileReaderReadyState {
     Empty = FileReaderConstants::EMPTY,
     Loading = FileReaderConstants::LOADING,
     Done = FileReaderConstants::DONE,
 }
 
-#[derive(HeapSizeOf, JSTraceable)]
+#[derive(JSTraceable, MallocSizeOf)]
 pub enum FileReaderResult {
     ArrayBuffer(Heap<JSVal>),
     String(DOMString),