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/websocket.rs

@@ -41,7 +41,7 @@ use task::{TaskOnce, TaskCanceller};
 use task_source::TaskSource;
 use task_source::networking::NetworkingTaskSource;
 
-#[derive(Clone, Copy, Debug, HeapSizeOf, JSTraceable, PartialEq)]
+#[derive(Clone, Copy, Debug, JSTraceable, MallocSizeOf, PartialEq)]
 enum WebSocketRequestState {
     Connecting = 0,
     Open = 1,
@@ -104,7 +104,7 @@ pub struct WebSocket {
     ready_state: Cell<WebSocketRequestState>,
     buffered_amount: Cell<u64>,
     clearing_buffer: Cell<bool>, //Flag to tell if there is a running thread to clear buffered_amount
-    #[ignore_heap_size_of = "Defined in std"]
+    #[ignore_malloc_size_of = "Defined in std"]
     sender: DomRefCell<Option<IpcSender<WebSocketDomAction>>>,
     binary_type: Cell<BinaryType>,
     protocol: DomRefCell<String>, //Subprotocol selected by server