New build flag system, convert Google Now flag

chrome/browser/BUILD.gn

Index: chrome/browser/BUILD.gn
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 8f194965e62a323ebb24031ad00e9f92d64d77bc..d09b1f22d26545a11eac3db08b791eb6267e4377 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -6,6 +6,7 @@ import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
+import("//chrome/common/features.gni")
 import("//media/media_options.gni")
 import("//third_party/protobuf/proto_library.gni")
 
@@ -957,6 +958,7 @@ if (is_win) {
 # (generate_browser_resources action)
 grit("resources") {
   source = "browser_resources.grd"
+  defines = chrome_grit_defines
   output_dir = "$root_gen_dir/chrome"
   outputs = [
     "grit/browser_resources.h",