Move toString() to collection classes.

sdk/lib/_collection_dev/iterable.dart

Index: sdk/lib/_collection_dev/iterable.dart
diff --git a/sdk/lib/_collection_dev/iterable.dart b/sdk/lib/_collection_dev/iterable.dart
index 82c6ebf12c6fb8300ba6bb17153e22e2de8d9d13..7013272c6ca420ddb7f99adf3b44859593143e73 100644
--- a/sdk/lib/_collection_dev/iterable.dart
+++ b/sdk/lib/_collection_dev/iterable.dart
@@ -688,6 +688,9 @@ abstract class BidirectionalIterator<T> implements Iterator<T> {
  * The uses of this class will be replaced by mixins.
  */
 class IterableMixinWorkaround {
+  // A list to identify cyclic collections during toString() calls.
+  static List _toStringList = new List();
+
   static bool contains(Iterable iterable, var element) {
     for (final e in iterable) {
       if (e == element) return true;
@@ -881,6 +884,27 @@ class IterableMixinWorkaround {
     return buffer.toString();
   }
 
+  static String toStringIterable(Iterable iterable, String leftDelimiter,
+                                 String rightDelimiter) {
+    for (int i = 0; i < _toStringList.length; i++) {
+      if (identical(_toStringList[i], iterable)) {
+        return '$leftDelimiter...$rightDelimiter';
+        }
+    }
+
+    StringBuffer result = new StringBuffer();
+    try {
+      _toStringList.add(iterable);
+      result.write(leftDelimiter);
+      result.writeAll(iterable, ', ');
+      result.write(rightDelimiter);
+    } finally {
+      assert(identical(_toStringList.last, iterable));
+      _toStringList.removeLast();
+    }
+    return result.toString();
+  }
+
   static Iterable where(Iterable iterable, bool f(var element)) {
     return new WhereIterable(iterable, f);
   }