[NaCl SDK} Add EventListener and EventEmitter to support epoll.

native_client_sdk/src/libraries/nacl_io_test/example.dsc

 {
   'TOOLS': ['newlib', 'glibc', 'pnacl', 'win'],
   'SEL_LDR': True,
 
   # Need to add ../../examples for common.js
   'SEARCH': ['.', '../../examples'],
   'TARGETS': [
     {
       'NAME' : 'nacl_io_test',
       'TYPE' : 'main',
       'SOURCES' : [
+        'event_test.cc',
         'kernel_object_test.cc',
         'kernel_proxy_mock.cc',
         'kernel_proxy_mock.h',
         'kernel_proxy_test.cc',
         'kernel_wrap_test.cc',
         'main.cc',
         'mock_util.h',
         'mount_html5fs_test.cc',
         'mount_http_test.cc',
         'mount_mock.cc',
@@ skipping 13 matching lines @@
       'INCLUDES': ['$(NACL_SDK_ROOT)/include/gtest/internal'],
     }
   ],
   'DATA': [
     'example.js'
   ],
   'DEST': 'tests',
   'NAME': 'nacl_io_test',
   'TITLE': 'NaCl IO test',
 }