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 bc8919653997bb889e57043eb0a195bacff08d8b..9b20bdab010bf41f951a7aa35c2a687e26a4076f 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/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")
@@ -36,6 +38,11 @@ if (enable_extensions) {
   }
 }
 
+buildflag_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:base_static",
     "//base:i18n",
@@ -315,6 +323,7 @@ static_library("constants") {
     "//content/public/common:result_codes",
   ]
   deps = [
+    ":features",
     ":version_header",
     "//base",
     "//base/third_party/dynamic_annotations",