New build flag system, convert Google Now flag

chrome/browser/ui/BUILD.gn

 # 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.
 
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
+import("//chrome/common/features.gni")
 
 gypi_values = exec_script("//build/gypi_to_gn.py",
                           [ rebase_path("../../chrome_browser_ui.gypi") ],
                           "scope",
                           [ "../../chrome_browser_ui.gypi" ])
 
 config("ui_warnings") {
   if (is_clang) {
     # TODO(thakis): Remove this once http://crbug.com/383820 is figured out
     cflags = [ "-Wno-nonnull" ]
@@ skipping 584 matching lines @@
     "//chrome/browser",
     "//content/public/browser",
     "//content/public/common",
     "//content/test:test_support",
     "//net:test_support",
     "//skia",
     "//testing/gtest",
     "//ui/base",
   ]
 }