Compact LinkedHashMap/Set implementation.

runtime/lib/collection_patch.dart

Index: runtime/lib/collection_patch.dart
===================================================================
--- runtime/lib/collection_patch.dart	(revision 43712)
+++ runtime/lib/collection_patch.dart	(working copy)
@@ -918,6 +918,8 @@
         if (equals == null) {
           if (_useInternalCached) {
             return new _InternalLinkedHashMap<K, V>();
+          } else if (_useCompactCached) {
+            return new _CompactLinkedHashMap<K, V>();
           } else {
             return new _LinkedHashMap<K, V>();
           }
@@ -947,6 +949,8 @@
 
   static final bool _useInternalCached = _useInternal;
   static bool get _useInternal native "LinkedHashMap_useInternal";
+  static final bool _useCompactCached = _useCompact;
+  static bool get _useCompact native "LinkedHashMap_useCompact";
 }
 
 // Methods that are exactly the same in all three linked hash map variants.
@@ -1063,7 +1067,11 @@
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
-          return new _LinkedHashSet<E>();
+          if (_useCompactCached) {

[Vyacheslav Egorov (Google), 2015/02/12 15:42:40]

Any reason why you can't just do LinkedHashMap._useCompactCached?

[koda, 2015/02/17 17:26:28]

Done.

+            return new _CompactLinkedHashSet<E>();
+          } else {
+            return new _LinkedHashSet<E>();
+          }
         }
         hashCode = _defaultHashCode;
       } else {
@@ -1087,6 +1095,9 @@
   }
 
   /* patch */ factory LinkedHashSet.identity() = _LinkedIdentityHashSet<E>;
+
+  static final bool _useCompactCached = _useCompact;
+  static bool get _useCompact native "LinkedHashMap_useCompact";
 }
 
 class _LinkedHashSetEntry extends _HashSetEntry {