Avoid unnecessary HashTable resizing during copy construction.

third_party/WebKit/Source/wtf/HashTable.h

 /*
  * Copyright (C) 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2008 David Levin <levin@chromium.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 1809 matching lines @@
 #if DCHECK_IS_ON()
       ,
       m_accessForbidden(false),
       m_modifications(0)
 #endif
 #if DUMP_HASHTABLE_STATS_PER_TABLE
       ,
       m_stats(HashTableStatsPtr<Allocator>::copy(other.m_stats))
 #endif
 {
+  if (other.size())
+    reserveCapacityForSize(other.size());
   // Copy the hash table the dumb way, by adding each element to the new
   // table.  It might be more efficient to copy the table slots, but it's not
   // clear that efficiency is needed.
-  const_iterator end = other.end();
-  for (const_iterator it = other.begin(); it != end; ++it)
-    add(*it);
+  for (const auto& element : other)
+    add(element);
 }
 
 template <typename Key,
           typename Value,
           typename Extractor,
           typename HashFunctions,
           typename Traits,
           typename KeyTraits,
           typename Allocator>
 HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::
@@ skipping 424 matching lines @@
   CollectionIterator end(toBeRemoved.end());
   for (CollectionIterator it(toBeRemoved.begin()); it != end; ++it)
     collection.erase(*it);
 }
 
 }  // namespace WTF
 
 #include "wtf/HashIterators.h"
 
 #endif  // WTF_HashTable_h