Put HashMap class in dart namespace.

runtime/platform/hashmap.cc

 // Copyright (c) 2012, 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.
 
 #include "platform/hashmap.h"
 
 #include "bin/builtin.h"
 #include "platform/utils.h"
 
-HashMap::HashMap(MatchFun match,
-                 uint32_t initial_capacity) {
+namespace dart {
+
+HashMap::HashMap(MatchFun match, uint32_t initial_capacity) {
   match_ = match;
   Initialize(initial_capacity);
 }
 
 
 HashMap::~HashMap() {
   free(map_);
 }
 
 
@@ skipping 159 matching lines @@
   for (Entry* p = map; n > 0; p++) {
     if (p->key != NULL) {
       Lookup(p->key, p->hash, true)->value = p->value;
       n--;
     }
   }
 
   // Delete old map.
   free(map);
 }
+
+}  // namespace dart