Remove the heapsize feature

It is not exposed, so never compiled. It's leftover from when
lru_disk_cache was a separate crate.

src/lru_disk_cache/lru_cache.rs

@@ -37,17 +37,6 @@
 //! assert!(cache.get_mut(&2).is_none());
 //! ```
 //!
-//! The cache can also be limited by an arbitrary metric calculated from its key-value pairs, see
-//! [`LruCache::with_meter`][with_meter] for more information. If the `heapsize` feature is enabled,
-//! this crate provides one such alternate metric—`HeapSize`. Custom metrics can be written by
-//! implementing the [`Meter`][meter] trait.
-//!
-//! [with_meter]: struct.LruCache.html#method.with_meter
-//! [meter]: trait.Meter.html
-
-#[cfg(feature = "heapsize")]
-extern crate heapsize;
-
 use std::borrow::Borrow;
 use std::collections::hash_map::RandomState;
 use std::fmt;
@@ -153,33 +142,6 @@ impl<K, V> CountableMeterWithMeasure<K, V, ()> for Count {
     }
 }
 
-#[cfg(feature = "heapsize")]
-mod heap_meter {
-    use heapsize::HeapSizeOf;
-    use std::borrow::Borrow;
-
-    /// Size limit based on the heap size of each cache item.
-    ///
-    /// Requires cache entries that implement [`HeapSizeOf`][1].
-    ///
-    /// [1]: https://doc.servo.org/heapsize/trait.HeapSizeOf.html
-    pub struct HeapSize;
-
-    impl<K, V: HeapSizeOf> super::Meter<K, V> for HeapSize {
-        type Measure = usize;
-
-        fn measure<Q: ?Sized>(&self, _: &Q, item: &V) -> usize
-        where
-            K: Borrow<Q>,
-        {
-            item.heap_size_of_children() + ::std::mem::size_of::<V>()
-        }
-    }
-}
-
-#[cfg(feature = "heapsize")]
-pub use heap_meter::*;
-
 /// An LRU cache.
 #[derive(Clone)]
 pub struct LruCache<K: Eq + Hash, V, S: BuildHasher = RandomState, M: CountableMeter<K, V> = Count>
@@ -906,19 +868,4 @@ mod tests {
         assert!(!cache.contains_key("foo1"));
         assert!(!cache.contains_key("foo2"));
     }
-
-    #[cfg(feature = "heapsize")]
-    #[test]
-    fn test_heapsize_cache() {
-        use super::HeapSize;
-
-        let mut cache = LruCache::<&str, (u8, u8, u8), _, _>::with_meter(8, HeapSize);
-        cache.insert("foo1", (1, 2, 3));
-        cache.insert("foo2", (4, 5, 6));
-        cache.insert("foo3", (7, 8, 9));
-        assert!(!cache.contains_key("foo1"));
-        cache.insert("foo2", (10, 11, 12));
-        cache.insert("foo4", (13, 14, 15));
-        assert!(!cache.contains_key("foo3"));
-    }
 }