Move ENABLE_HIDPI to new build flags system

ui/base/ui_base.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': [
     {
@@ skipping 23 matching lines @@
       'defines': [
         'UI_DATA_PACK_IMPLEMENTATION',
       ],
       'conditions': [
         ['OS=="win"', {
           # TODO(jschuh): C4267: http://crbug.com/167187 size_t -> int
           'msvs_disabled_warnings': [ 4267 ],
         }],
     ],
     },
+    { # GN version: //ui/base:ui_features
+      'target_name': 'ui_features',
+      'includes': [ '../../build/buildflag_header.gypi' ],
+      'variables': {
+        'buildflag_header_path': 'ui/base/ui_features.h',
+        'buildflag_flags': [
+          'ENABLE_HIDPI=<(enable_hidpi)',
+        ],
+      },
+    },
     {
       # GN version: //ui/base
       'target_name': 'ui_base',
       'type': '<(component)',
       'dependencies': [
         'ui_data_pack',
+        'ui_features',
         '../../base/base.gyp:base',
         '../../base/base.gyp:base_i18n',
         '../../base/base.gyp:base_static',
         '../../base/third_party/dynamic_annotations/dynamic_annotations.gyp:dynamic_annotations',
         '../../net/net.gyp:net',
         '../../skia/skia.gyp:skia',
         '../../third_party/icu/icu.gyp:icui18n',
         '../../third_party/icu/icu.gyp:icuuc',
         '../../url/url.gyp:url_lib',
         '../events/events.gyp:events',
@@ skipping 700 matching lines @@
            ],
            'variables': {
              'jni_gen_package': 'ui',
            },
            'includes': [ '../../build/jni_generator.gypi' ],
          },
        ],
     }],
   ],
 }