Provide a mechanism for naming a hash table so that it can be used in DumpStats to identify the tab…

runtime/vm/hash_table_test.cc

Index: runtime/vm/hash_table_test.cc
diff --git a/runtime/vm/hash_table_test.cc b/runtime/vm/hash_table_test.cc
index b646b32117d2f75d82c20a679e325f57c87eff56..f4139324c12535d990be9a8f9c048436113b76b0 100644
--- a/runtime/vm/hash_table_test.cc
+++ b/runtime/vm/hash_table_test.cc
@@ -20,6 +20,8 @@ namespace dart {
 // easy to engineer collisions.
 class TestTraits {
  public:
+  static const char* Name() { return "TestTraits"; }
+
   static bool IsMatch(const char* key, const Object& obj) {
     return String::Cast(obj).Equals(key);
   }