Use hash map for event handler file descriptor map

runtime/bin/builtin_sources.gypi

 # 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.
 
 # This file contains all sources (vm and tests) for the dart virtual machine.
 # Unit test files need to have a '_test' suffix appended to the name.
 {
   'sources': [
     #
     # Dart sources.
@@ skipping 39 matching lines @@
     'eventhandler_win.h',
     'file.cc',
     'file.h',
     'file_linux.cc',
     'file_macos.cc',
     'file_win.cc',
     'file_test.cc',
     'fdutils.h',
     'fdutils_linux.cc',
     'fdutils_macos.cc',
+    'hashmap.cc',
+    'hashmap.h',
+    'hashmap_test.cc',
     'platform.cc',
     'platform.h',
     'platform_linux.cc',
     'platform_macos.cc',
     'platform_win.cc',
     'process.cc',
     'process.h',
     'process_linux.cc',
     'process_macos.cc',
     'process_win.cc',
     'socket.cc',
     'socket.h',
     'socket_linux.cc',
     'socket_macos.cc',
     'socket_win.cc',
     'set.h',
     'set_test.cc',
     'thread.h',
     'thread_pool.cc',
     'thread_pool_linux.cc',
     'thread_pool_linux.h',
     'thread_pool_macos.cc',
     'thread_pool_macos.h',
     'thread_pool_test.cc',
     'thread_pool_win.cc',
     'thread_pool_win.h',
   ],
 }