Overhaul MallocSizeOf and related things.

This patch makes the MallocSizeOf stuff in Stylo work more like the HeapSizeOf
stuff already in Servo, except better. In particular, it adds deriving support
for MallocSizeOf, which will make it easier to improve coverage.

The patch does the following.

- Combines servo/components/style/stylesheets/memory.rs and the heapsize crate
  into a new crate, malloc_size_of.

- Forks the heapsize_derive crate, calling it malloc_size_of, so that
  MallocSizeOf can be derived.

- Both the new crates have MIT/Apache licenses, like heapsize, in case they are
  incorporated into heapsize in the future.

- Renames the methods within MallocSizeOf and the related traits so they are
  more concise.

- Removes MallocSizeOfWithGuard.

- Adds `derive(MallocSizeOf)` to a lot of types, in some cases replacing an
  equivalent or almost-equivalent hand-written implementation.

- Adds stuff so that Rc/Arc can be handled properly.

components/style/invalidation/media_queries.rs

@@ -8,7 +8,7 @@ use context::QuirksMode;
 use fnv::FnvHashSet;
 use media_queries::Device;
 use shared_lock::SharedRwLockReadGuard;
-use stylesheets::{DocumentRule, ImportRule, MallocEnclosingSizeOfFn, MallocSizeOfHash, MediaRule};
+use stylesheets::{DocumentRule, ImportRule, MediaRule};
 use stylesheets::{NestedRuleIterationCondition, Stylesheet, SupportsRule};
 
 /// A key for a given media query result.
@@ -24,6 +24,7 @@ use stylesheets::{NestedRuleIterationCondition, Stylesheet, SupportsRule};
 /// If this changes, though, we may need to remove the item from the cache if
 /// present before it goes away.
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct MediaListKey(usize);
 
@@ -53,6 +54,7 @@ impl ToMediaListKey for MediaRule {}
 /// A struct that holds the result of a media query evaluation pass for the
 /// media queries that evaluated successfully.
 #[derive(Debug)]
+#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct EffectiveMediaQueryResults {
     /// The set of media lists that matched last time.
@@ -88,12 +90,6 @@ impl EffectiveMediaQueryResults {
         // because of stylesheet reusing... shrug.
         self.set.insert(item.to_media_list_key());
     }
-
-    /// Measure heap usage.
-    pub fn malloc_size_of_children(&self, malloc_enclosing_size_of: MallocEnclosingSizeOfFn)
-                                   -> usize {
-        self.set.malloc_shallow_size_of_hash(malloc_enclosing_size_of)
-    }
 }
 
 /// A filter that filters over effective rules, but allowing all potentially