Put HashMap class in dart namespace.

runtime/bin/hashmap_test.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/assert.h"
 #include "platform/globals.h"
 #include "platform/hashmap.h"
 #include "vm/unit_test.h"
 
+namespace dart {
+
 // Default initial size of hashmaps used in these tests.
 static intptr_t kInitialSize = 8;
 
 
 typedef uint32_t (*IntKeyHash)(uint32_t key);
 
 
 class IntSet {
  public:
   explicit IntSet(IntKeyHash hash)
@@ skipping 140 matching lines @@
 
 
 UNIT_TEST_CASE(Set) {
   TestSet(WordHash, 100);
   TestSet(Hash, 100);
   TestSet(CollisionHash1, 50);
   TestSet(CollisionHash2, 50);
   TestSet(CollisionHash3, 50);
   TestSet(CollisionHash4, 50);
 }
+
+}  // namespace dart