Create EarlGrey wait utility.

ios/testing/earl_grey/earl_grey_support.gyp

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
       # GN version: //ios/testing/earl_grey:earl_grey_support
       'target_name': 'earl_grey_support',
       'type': 'static_library',
+      'dependencies': [
+        '<(DEPTH)/ios/third_party/earl_grey/earl_grey.gyp:EarlGrey',
+      ],
       'sources': [
         'wait_util.h',
         'wait_util.mm',
       ],
       'include_dirs': [
         '../../..',
       ],
     },
   ],
 }