New build flag system, convert Google Now flag

chrome/common/BUILD.gn

Index: chrome/common/BUILD.gn
diff --git a/chrome/common/BUILD.gn b/chrome/common/BUILD.gn
index 01e134cbb98f0155b819e5263d1d4503d796e30d..22169b6d53fa984ad2645cd16699c8c16e47433b 100644
--- a/chrome/common/BUILD.gn
+++ b/chrome/common/BUILD.gn
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/build_header.gni")
+import("//chrome/common/features.gni")
 import("//chrome/version.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//tools/grit/grit_rule.gni")
@@ -36,6 +38,11 @@ if (enable_extensions) {
   }
 }
 
+build_header("features") {
+  header = "features.h"
+  flags = [ "ENABLE_GOOGLE_NOW=$enable_google_now" ]
+}
+
 # GYP version: chrome/chrome_common.gypi:common
 static_library("common") {
   sources = rebase_path(gypi_values.chrome_common_sources, ".", "//chrome")
@@ -47,6 +54,7 @@ static_library("common") {
   ]
 
   public_deps = [
+    ":features",
     "//base:base",
     "//base:i18n",
     "//base:prefs",
@@ -314,6 +322,7 @@ static_library("constants") {
     "//content/public/common:result_codes",
   ]
   deps = [
+    ":features",
     ":version_header",
     "//base",
     "//base/third_party/dynamic_annotations",