Reland "Merge more Kernel infrastructure from kernel_sdk SDK fork."

runtime/lib/compact_hash.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:typed_data';
-import 'dart:_internal' as internal;
-
 // Hash table with open addressing that separates the index from keys/values.
 
 abstract class _HashFieldBase {
   // Each occupied entry in _index is a fixed-size integer that encodes a pair:
   //   [ hash pattern for key | index of entry in _data ]
   // The hash pattern is based on hashCode, but is guaranteed to be non-zero.
   // The length of _index is always a power of two, and there is always at
   // least one unoccupied entry.
   // NOTE: When maps are deserialized, their _index and _hashMask is regenerated
   // lazily by _regenerateIndex.
@@ skipping 574 matching lines @@
   E lookup(Object o) => _validKey(o) ? super.lookup(o) : null;
   bool remove(Object o) => _validKey(o) ? super.remove(o) : false;
 
   _CompactLinkedCustomHashSet(this._equality, this._hasher, validKey)
       : _validKey = (validKey != null) ? validKey : new _TypeTest<E>().test;
 
   Set<E> toSet() =>
       new _CompactLinkedCustomHashSet<E>(_equality, _hasher, _validKey)
           ..addAll(this);
 }