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/malloc_size_of/Cargo.toml

@@ -8,11 +8,22 @@ publish = false
 [lib]
 path = "lib.rs"
 
+[target.'cfg(windows)'.dependencies]
+kernel32-sys = "0.2.1"
+
+[features]
+servo = ["js", "string_cache", "url", "webrender_api", "xml5ever"]
+
 [dependencies]
 app_units = "0.5.5"
 cssparser = "0.22.0"
 euclid = "0.15"
 hashglobe = { path = "../hashglobe" }
+js = { git = "https://github.com/servo/rust-mozjs", features = ["promises"], optional = true }
 servo_arc = { path = "../servo_arc" }
 smallbitvec = "1.0.3"
 smallvec = "0.4"
+string_cache = { version = "0.6", optional = true }
+url = { version = "1.2", optional = true }
+webrender_api = { git = "https://github.com/servo/webrender", features = ["ipc"], optional = true }
+xml5ever = { version = "0.10", optional = true }