New build flag system, convert Google Now flag

chrome/chrome_common.gypi

Index: chrome/chrome_common.gypi
diff --git a/chrome/chrome_common.gypi b/chrome/chrome_common.gypi
index 6694ccabf4f467b0c92584e6dee78b03a2b3121a..71a903c7a005b2f5e9612cb73912c9284b77525e 100644
--- a/chrome/chrome_common.gypi
+++ b/chrome/chrome_common.gypi
@@ -314,6 +314,7 @@
         # TODO(gregoryd): chrome_resources and chrome_strings could be
         #  shared with the 64-bit target, but it does not work due to a gyp
         # issue.
+        'chrome_common_features',
         'installer_util',
         'safe_browsing_proto',
         '<(DEPTH)/base/base.gyp:base',
@@ -562,6 +563,7 @@
         'common/net/x509_certificate_model_openssl.cc',
       ],
       'dependencies': [
+        'chrome_common_features',
         '<(DEPTH)/base/base.gyp:base',
         '<(DEPTH)/chrome/chrome_resources.gyp:chrome_resources',
         '<(DEPTH)/chrome/chrome_resources.gyp:chrome_strings',
@@ -651,5 +653,16 @@
         '../third_party/mojo/mojo_public.gyp:mojo_cpp_bindings',
       ],
     },
+    {
+      # GN version: //chrome/common:features
+      'target_name': 'chrome_common_features',
+      'includes': [ '../build/build_header.gypi' ],
+      'variables': {
+        'build_header_path': 'chrome/common/features.h',
+        'build_header_flags': [
+          'ENABLE_GOOGLE_NOW=<(enable_google_now)',
+        ],
+      },
+    },
   ],
 }