diff --git a/accepted/future-releases/spread-collections/benchmarks/bin/lrhn_benchmark.dart b/accepted/future-releases/spread-collections/benchmarks/bin/lrhn_benchmark.dart
new file mode 100644
index 0000000000..a254e5f5fe
--- /dev/null
+++ b/accepted/future-releases/spread-collections/benchmarks/bin/lrhn_benchmark.dart
@@ -0,0 +1,53 @@
+import"dart:collection";
+void copy1(Map<String, int> from, Map<String, int> to) {
+  for (var entry in from.entries) {
+    to[entry.key] = entry.value;
+  }
+}
+void copy2(Map<String, int> from, Map<String, int> to) {
+  for (var key in from.keys) {
+    to[key] = from[key];
+  }
+}
+void copy3(Map<String, int> from, Map<String, int> to) {
+  var tmp = to;
+  from.forEach((key, value) {
+    tmp[key] = value;
+  });
+  tmp = null;
+}
+void copy4(Map<String, int> from, Map<String, int> to) {
+  to.addAll(from);
+}
+
+main() {
+  for (int i = 0; i < 5; i++) {
+    bench("entries", copy1);
+    bench("keys", copy2);
+    bench("forEach", copy3);
+    bench("addAll", copy4);
+  }
+}
+
+int id(int x)=>x;
+var maps = List.generate(100, (n) {
+  var map = Map<String, int>.fromIterable(Iterable.generate(n * 10), key: (n) =>"#$n");
+  if (n % 4 == 1) map = SplayTreeMap<String, int>.from(map);
+  if (n % 4 == 2) map = HashMap<String, int>.from(map);
+  return map;
+});
+
+void bench(String name, void Function(Map<String, int>, Map<String, int>) action) {
+  var e = 0;
+  var c = 0;
+  var sw = Stopwatch()..start();
+  do {
+    for (var from in maps) {
+      var to = <String, int>{};
+      action(from, to);
+      c += from.length;
+    }
+    e = sw.elapsedMilliseconds;
+  } while (e < 2000);
+  print("$name: ${c/e} entries/ms");
+}
diff --git a/accepted/future-releases/spread-collections/benchmarks/bin/profile_map.dart b/accepted/future-releases/spread-collections/benchmarks/bin/profile_map.dart
new file mode 100644
index 0000000000..e569ac0762
--- /dev/null
+++ b/accepted/future-releases/spread-collections/benchmarks/bin/profile_map.dart
@@ -0,0 +1,302 @@
+import 'dart:collection';
+
+const trials = 2000;
+const rounds = 4;
+
+var csv = StringBuffer();
+
+bool warmup = true;
+
+//class CustomMap<K, V> extends MapBase<K, V> {
+//  final Map<K, V> _inner;
+//
+//  CustomMap(this._inner);
+//
+//  operator [](Object key) => _inner[key];
+//
+//  void operator []=(key, value) => _inner[key] = value;
+//
+//  void clear() => throw "not implemented";
+//
+//  Iterable<K> get keys => _inner.keys;
+//
+//  remove(Object key) => throw "not implemented";
+//}
+
+void main() {
+  benchmarks();
+}
+
+void benchmarks() {
+  final maps = makeMaps([0, 1, 2, 5, 10, 20, 50, 100], (map) {
+    return [
+      map,
+      SplayTreeMap.of(map),
+      HashMap.of(map),
+    ];
+  });
+
+  for (var i = 1; i <= rounds; i++) {
+    warmup = i < rounds;
+
+    var baseline = bench("addEntries", maps, addEntries);
+    var entriesMap =
+        bench("iterate entries into map", maps, iterateEntriesIntoNewMap, baseline);
+    var keysMap = bench("iterate keys into map", maps, iterateKeysIntoNewMap, baseline);
+    var forEachMap = bench("forEach into map", maps, forEachIntoNewMap, baseline);
+
+    log();
+
+    var justEntries = bench("just iterate entries", maps, iterateEntries);
+    var justKeys = bench("just iterate keys", maps, iterateKeys);
+    var justForEach = bench("just forEach", maps, forEach);
+
+    log();
+
+    log("(entries insertion overhead)", entriesMap - justEntries);
+    log("(keys insertion overhead)", keysMap - justKeys);
+    log("(forEach insertion overhead)", forEachMap - justForEach);
+  }
+}
+
+Map<String, int> makeMap(int size) {
+  var result = <String, int>{};
+  for (var i = 0; i < size; i++) {
+    var key = "";
+    var n = i + 1;
+    while (n > 0) {
+      key += String.fromCharCode((n % 26) + 65);
+      n ~/= 26;
+    }
+
+    result[key] = i;
+  }
+
+  return result;
+}
+
+List<Map<String, int>> makeMaps(List<int> sizes,
+    List<Map<String, int>> Function(Map<String, int>) callback) {
+  var maps = <Map<String, int>>[];
+  for (var size in sizes) {
+    var map = makeMap(size);
+    maps.addAll(callback(map));
+  }
+
+  return maps;
+}
+
+double bench(String label, List<Map<String, int>> maps,
+    void Function(Map<String, int>) action, [double baseline]) {
+  var watch = Stopwatch()..start();
+  for (var i = 0; i < trials; i++) {
+    for (var i = 0; i < maps.length; i++) {
+      action(maps[i]);
+    }
+  }
+
+  watch.stop();
+  var microPerTrial = watch.elapsedMicroseconds / (trials * maps.length);
+  log(label, microPerTrial, baseline);
+  return microPerTrial;
+}
+
+void log([String label, double microseconds, double baseline]) {
+  if (warmup) return;
+
+  if (microseconds != null) {
+    var perMs = (1000 / microseconds).toStringAsFixed(2);
+    var output = "${label.padLeft(30)} ${perMs.padLeft(10)} spreads/ms";
+    if (baseline != null) {
+      var relative = baseline / microseconds;
+      output += " ${relative.toStringAsFixed(2).padLeft(5)}x";
+    }
+    print(output);
+  } else if (label != null) {
+    print("--- $label ---");
+  } else {
+    print("");
+  }
+}
+
+void iterateEntries(Map<String, int> from) {
+  var sum = 0;
+  for (var entry in from.entries) {
+    sum += entry.value;
+  }
+
+  preventOptimization(sum);
+}
+
+void iterateEntriesIntoNewMap(Map<String, int> from) {
+  var to = <String, int>{"a": 1, "b": 2};
+
+  for (var entry in from.entries) {
+    to[entry.key] = entry.value;
+  }
+
+  to["b"] = 3;
+  to["c"] = 4;
+
+  preventOptimization(to.length);
+}
+
+void iterateKeys(Map<String, int> from) {
+  var sum = 0;
+  for (var key in from.keys) {
+    sum += from[key];
+  }
+
+  preventOptimization(sum);
+}
+
+void iterateKeysIntoNewMap(Map<String, int> from) {
+  var to = <String, int>{"a": 1, "b": 2};
+
+  for (var key in from.keys) {
+    to[key] = from[key];
+  }
+
+  to["b"] = 3;
+  to["c"] = 4;
+
+  preventOptimization(to.length);
+}
+
+void forEach(Map<String, int> from) {
+  var sum = 0;
+  from.forEach((key, value) {
+    sum += value;
+  });
+
+  preventOptimization(sum);
+}
+
+void forEachIntoNewMap(Map<String, int> from) {
+  var to = <String, int>{"a": 1, "b": 2};
+
+  var temp = to;
+  from.forEach((key, value) {
+    temp[key] = value;
+  });
+  temp = null;
+
+  to["b"] = 3;
+  to["c"] = 4;
+
+  preventOptimization(to.length);
+}
+
+void addEntries(Map<String, int> from) {
+  var to = <String, int>{"a": 1, "b": 2};
+
+  to.addEntries(from.entries);
+
+  to["b"] = 3;
+  to["c"] = 4;
+
+  preventOptimization(to.length);
+}
+
+/// Ensure [obj] is used in some way so that the optimizer doesn't eliminate
+/// the code that produces it.
+void preventOptimization(Object obj) {
+  if (obj == "it will never be this") print("!");
+}
+
+//double runBench(String name, int length,
+//    void Function(Map<String, int>, Map<String, int>) action,
+//    [double baseline]) {
+//  var from = <String, int>{};
+//  for (var i = 0; i < length; i++) {
+//    from[String.fromCharCode(i % 26 + 65)] = i;
+//  }
+//
+//  var froms = [from, CustomMap(from)];
+//
+//  var rate = benchBest(froms, action);
+//
+//  if (baseline == null) {
+//    print("${length.toString().padLeft(4)} ${name.padRight(15)} "
+//        "${rate.toStringAsFixed(2).padLeft(10)} spreads/ms "
+//        "                 ${'-' * 20}");
+//  } else {
+//    var comparison = rate / baseline;
+//    var bar = "=" * (comparison * 20).toInt();
+//    if (comparison > 4.0) bar = "!!!";
+//    print("${length.toString().padLeft(4)} ${name.padRight(15)} "
+//        "${rate.toStringAsFixed(2).padLeft(10)} spreads/ms "
+//        "${comparison.toStringAsFixed(2).padLeft(6)}x baseline $bar");
+//  }
+//
+//  csv.writeln("$length,$name,$rate");
+//  return rate;
+//}
+//
+///// Runs [bench] a number of times and returns the best (highest) result.
+//double benchBest(List<Map<String, int>> froms,
+//    void Function(Map<String, int>, Map<String, int>) action) {
+//  var best = 0.0;
+//  for (var i = 0; i < 4; i++) {
+//    var result = bench(froms, action);
+//    if (result > best) best = result;
+//  }
+//
+//  return best;
+//}
+//
+//double bench(List<Map<String, int>> froms,
+//    void Function(Map<String, int>, Map<String, int>) action) {
+//  var elapsed = 0;
+//  var count = 0;
+//  var watch = Stopwatch()..start();
+//  do {
+//    for (var i = 0; i < froms.length; i++) {
+//      var from = froms[i];
+//      var to = <String, int>{"a": 1, "b": 2};
+//
+//      action(from, to);
+//      to["b"] = 3;
+//      to["c"] = 4;
+//
+//      count++;
+//    }
+//    elapsed = watch.elapsedMilliseconds;
+//  } while (elapsed < trialMs);
+//
+//  return count / elapsed;
+//}
+//
+//void iterateEntries(Map<String, int> from, Map<String, int> to) {
+//  for (var entry in from.entries) {
+//    to[entry.key] = entry.value;
+//  }
+//}
+
+//void addList(Map<String, int> from, Map<String, int> to) {
+//  var length = from.length;
+//  for (var i = 0; i < length; i++) {
+//    to.add(from[i]);
+//  }
+//}
+//
+//void resizeAndSet(Map<String, int> from, Map<String, int> to) {
+//  var length = from.length;
+//  var j = to.length;
+//  to.length = to.length + length;
+//  for (var i = 0; i < length; i++) {
+//    to[j] = from[i];
+//  }
+//}
+//
+//void addAll(Map<String, int> from, Map<String, int> to) {
+//  to.addAll(from);
+//}
+//
+//void forEach(Map<String, int> from, Map<String, int> to) {
+//  var temp = to;
+//  from.forEach((s) {
+//    temp.add(s);
+//  });
+//  temp = null;
+//}