Convert enable_one_click_signin to new buildflag system

chrome/common/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/buildflag_header.gni")
 import("//chrome/common/features.gni")
 import("//chrome/version.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//tools/grit/grit_rule.gni")
 
@@ skipping 24 matching lines @@
       "grit/extensions_api_resources.h",
       "extensions_api_resources.pak",
     ]
   }
 }
 
 buildflag_header("features") {
   header = "features.h"
   flags = [
     "ENABLE_GOOGLE_NOW=$enable_google_now",
+    "ENABLE_ONE_CLICK_SIGNIN=$enable_one_click_signin",
     "ANDROID_JAVA_UI=$android_java_ui",
     "USE_VULCANIZE=$use_vulcanize",
   ]
 }
 
 # GYP version: chrome/chrome_common.gypi:common
 static_library("common") {
   sources = rebase_path(gypi_values.chrome_common_sources, ".", "//chrome")
   defines = []
 
@@ skipping 338 matching lines @@
     ":constants",
     "//base",
   ]
 }
 
 mojom("mojo_bindings") {
   sources = [
     "resource_usage_reporter.mojom",
   ]
 }