New build flag system, convert Google Now flag

This generates headers with build flags rather than forcing them all to be global. It includes an accessor wrapper so that references to the flags will fail if the proper header is not included.

Converts Google Now to use this and remove the global google now define and grit define.

Adds support for grit define values of "true" and "false" for ease of integration with GN (they are mapped to the corresponding Python "True" and "False").

Adds dependencies from the main gyp targets to the new generated feature define target. Since GYP only does hard dependencies one level, this should reduce the chance that somebody adds more of these cases and forces to add a dependency.

Review URL: https://codereview.chromium.org/1458653002

Cr-Commit-Position: refs/heads/master@{#361527}

36 files changed, 525 insertions, 38 deletions

diff --git a/build/buildflag.h b/build/buildflag.h
new file mode 100644
index 0000000..283f5bc
--- /dev/null
+++ b/build/buildflag.h
@@ -0,0 +1,47 @@
+// Copyright 2015 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.
+
+#ifndef BUILD_BUILDFLAG_H_
+#define BUILD_BUILDFLAG_H_
+
+// These macros un-mangle the names of the build flags in a way that looks
+// natural, and gives errors if the flag is not defined. Normally in the
+// preprocessor it's easy to make mistakes that interpret "you haven't done
+// the setup to know what the flag is" as "flag is off". Normally you would
+// include the generated header rather than include this file directly.
+//
+// This is for use with generated headers. See build/build_header.gni.
+
+// This dance of two macros does a concatenation of two preprocessor args using
+// ## doubly indirectly because using ## directly prevents macros in that
+// parameter from being expanded.
+#define BUILDFLAG_CAT_INDIRECT(a, b) a ## b
+#define BUILDFLAG_CAT(a, b) BUILDFLAG_CAT_INDIRECT(a, b)
+
+// Accessor for build flags.
+//
+// To test for a value, if the build file specifies:
+//
+//   ENABLE_FOO=true
+//
+// Then you would check at build-time in source code with:
+//
+//   #include "foo_flags.h"  // The header the build file specified.
+//
+//   #if BUILDFLAG(ENABLE_FOO)
+//     ...
+//   #endif
+//
+// There will no #define called ENABLE_FOO so if you accidentally test for
+// whether that is defined, it will always be negative. You can also use
+// the value in expressions:
+//
+//   const char kSpamServerName[] = BUILDFLAG(SPAM_SERVER_NAME);
+//
+// Because the flag is accessed as a preprocessor macro with (), an error
+// will be thrown if the proper header defining the internal flag value has
+// not been included.
+#define BUILDFLAG(flag) (BUILDFLAG_CAT(BUILDFLAG_INTERNAL_, flag)())
+
+#endif  // BUILD_BUILDFLAG_H_
diff --git a/build/buildflag_header.gni b/build/buildflag_header.gni
new file mode 100644
index 0000000..9054d07
--- /dev/null
+++ b/build/buildflag_header.gni
@@ -0,0 +1,138 @@
+# Copyright 2015 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.
+
+# Generates a header with preprocessor defines specified by the build file.
+# The GYP version of this (with instructions) is build/buildflag_header.gypi.
+#
+# The flags are converted to function-style defines with mangled names and
+# code uses an accessor macro to access the values. This is to try to
+# minimize bugs where code checks whether something is defined or not, and
+# the proper header isn't included, meaning the answer will always be silently
+# false or might vary across the code base.
+#
+# In the GN template, specify build flags in the template as a list
+# of strings that encode key/value pairs like this:
+#
+#   flags = [ "ENABLE_FOO=1", "ENABLE_BAR=$enable_bar" ]
+#
+# The GN values "true" and "false" will be mapped to 0 and 1 for boolean
+# #if flags to be expressed naturally. This means you can't directly make a
+# define that generates C++ value of true or false for use in code. If you
+# REALLY need this, you can also use the string "(true)" and "(false)" to
+# prevent the rewriting.
+
+# To check the value of the flag in C code:
+#
+#   #include "path/to/here/header_file.h"
+#
+#   #if BUILDFLAG(ENABLE_FOO)
+#   ...
+#   #endif
+#
+#   const char kSpamServerUrl[] = BUILDFLAG(SPAM_SERVER_URL);
+#
+# There will no #define called ENABLE_FOO so if you accidentally test for that
+# in an ifdef it will always be negative.
+#
+#
+# Template parameters
+#
+#   flags [required, list of strings]
+#       Flag values as described above.
+#
+#   header [required, string]
+#       File name for generated header. By default, this will go in the
+#       generated file directory for this target, and you would include it
+#       with:
+#         #include "<path_to_this_BUILD_file>/<header>"
+#
+#   header_dir [optional, string]
+#       Override the default location of the generated header. The string will
+#       be treated as a subdirectory of the root_gen_dir. For example:
+#         header_dir = "foo/bar"
+#       Then you can include the header as:
+#         #include "foo/bar/baz.h"
+#
+#   deps, public_deps, testonly, visibility
+#       Normal meaning.
+#
+#
+# Grit defines
+#
+# If one .grd file uses a flag, just add to the grit target:
+#
+#   defines = [
+#     "enable_doom_melon=$enable_doom_melon",
+#   ]
+#
+# If multiple .grd files use it, you'll want to put the defines in a .gni file
+# so it can be shared. Generally this .gni file should include all grit defines
+# for a given module (for some definition of "module"). Then do:
+#
+#   defines = ui_grit_defines
+#
+# If you forget to do this, the flag will be implicitly false in the .grd file
+# and those resources won't be compiled. You'll know because the resource
+# #define won't be generated and any code that uses it won't compile. If you
+# see a missing IDS_* string, this is probably the reason.
+#
+#
+# Example
+#
+#   buildflag_header("foo_features") {
+#     header = "foo_features.h"
+#
+#     flags = [
+#       # This uses the GN build flag enable_doom_melon as the definition.
+#       "ENABLE_DOOM_MELON=$enable_doom_melon",
+#
+#       # This force-enables the flag.
+#       "ENABLE_SPACE_LASER=true",
+#
+#       # This will expand to the quoted C string when used in source code.
+#       "SPAM_SERVER_URL=\"http://www.example.com/\"",
+#     ]
+#   }
+template("buildflag_header") {
+  action(target_name) {
+    script = "//build/write_buildflag_header.py"
+
+    if (defined(invoker.header_dir)) {
+      header_file = "${invoker.header_dir}/${invoker.header}"
+    } else {
+      # Compute the path from the root to this file.
+      header_file = rebase_path(".", "//") + "/${invoker.header}"
+    }
+
+    outputs = [
+      "$root_gen_dir/$header_file",
+    ]
+
+    # Always write --flags to the file so it's not empty. Empty will confuse GN
+    # into thinking the response file isn't used.
+    response_file_contents = [ "--flags" ]
+    if (defined(invoker.flags)) {
+      response_file_contents += invoker.flags
+    }
+
+    args = [
+      "--output",
+      header_file,  # Not rebased, Python script puts it inside gen-dir.
+      "--rulename",
+      get_label_info(":$target_name", "label_no_toolchain"),
+      "--gen-dir",
+      rebase_path(root_gen_dir, root_out_dir),
+      "--definitions",
+      "{{response_file_name}}",
+    ]
+
+    forward_variables_from(invoker,
+                           [
+                             "deps",
+                             "public_deps",
+                             "testonly",
+                             "visibility",
+                           ])
+  }
+}
diff --git a/build/buildflag_header.gypi b/build/buildflag_header.gypi
new file mode 100644
index 0000000..730ef429
--- /dev/null
+++ b/build/buildflag_header.gypi
@@ -0,0 +1,118 @@
+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Generates a header with preprocessor defines specified by the build file.
+#
+# The canonical documentation is in build/buildflag_header.gni. You should
+# write the GN build, get it working, and then transform it into GYP.
+#
+# In every target that uses your generated header you must include a dependency
+# on the GYP target that generates the header (this is implicit in GN).
+# Otherwise, clean builds may not necessarily create the header before the
+# source code is compiled.
+#
+# Assuming your GN code looks like this:
+#
+#   buildflag_header("foo_features") {
+#     header = "foo_features.h"
+#     flags = [
+#       "ENABLE_DOOM_MELON=$enable_doom_melon",
+#       "ENABLE_SPACE_LASER=true",
+#       "SPAM_SERVER_URL=\"http://www.example.com/\"",
+#     ]
+#   }
+#
+# Write a GYP target like this:
+#
+#  {
+#    # GN version: //foo:foo_features
+#    'target_name': 'foo_foo_features',
+#    'includes': [ '../build/buildflag_header.gypi' ],
+#    'variables': {
+#       'buildflag_header_path': 'foo/foo_features.h',
+#       'buildflag_header_flags': [
+#         'ENABLE_DOOM_MELON=<(enable_doom_melon)',
+#         'ENABLE_SPACE_LASER=true',
+#         'SPAM_SERVER_URL="http://www.example.com/"',
+#       ],
+#     },
+#   }
+#
+# Variables
+#
+#   target_name
+#       Base this on the GN label, replacing / and : with _ to make it globally
+#       unique.
+#
+#   buildflag_header_path
+#       This must be the full path to the header from the source root. In GN
+#       you only say "features.h" and it uses the BUILD file's path implicitly.
+#       Use the path to BUILD.gn followed by your header name to produce the
+#       same output file.
+#
+#   buildflag_flags (optional)
+#       List of the same format as GN's "flags". To expand variables, use
+#       "<(foo)" where GN would have used "$foo".
+#
+#   includes
+#       List the relative path to build/buildflag_header.gypi from the .gyp
+#       file including this code, Note: If your code is in a .gypi file in a
+#       different directory, this must be relative to the .gyp including your
+#       file.
+#
+#
+# Grit defines
+#
+# Follow the same advice as in the buildflag_header.gni, except on the grit
+# action use the variable name 'grit_additional_defines' and explicitly add a
+# '-D' in front:
+#
+#   'grit_grd_file': 'foo.grd',
+#   'grit_additional_defines': [
+#     '-D', 'enable_doom_melon=<(enable_doom_melon)',
+#    ],
+#
+# Put shared lists of defines in a .gypi.
+
+{
+  'type': 'none',
+  'hard_dependency': 1,
+
+  'actions': [
+    {
+      'action_name': 'buildflag_header',
+      'variables': {
+        # Default these values to empty if they're not defined.
+        'variables': {
+          'buildflag_flags%': [],
+        },
+
+        # Writes the flags to a response file with a name based on the name of
+        # this target.
+        'response_file_name': '<|(<(_target_name)_buildflag_header.rsp --flags <@(buildflag_flags))',
+
+        'build_header_script': '<(DEPTH)/build/write_buildflag_header.py',
+      },
+
+      'message': 'Generating build header.',
+
+      'inputs': [
+        '<(build_header_script)',
+        '<(response_file_name)',
+      ],
+
+      'outputs': [
+        '<(SHARED_INTERMEDIATE_DIR)/<(buildflag_header_path)',
+      ],
+
+      'action': [
+        'python', '<(build_header_script)',
+        '--output', '<(buildflag_header_path)',
+        '--rulename', '<(_target_name)',
+        '--gen-dir', '<(SHARED_INTERMEDIATE_DIR)',
+        '--definitions', '<(response_file_name)',
+      ],
+    }
+  ],
+}
diff --git a/build/common.gypi b/build/common.gypi
index 845ab5a..2a10d84 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -547,9 +547,6 @@
       # Enable Chrome browser extensions
       'enable_extensions%': 1,
 
-      # Enable Google Now.
-      'enable_google_now%': 1,
-
       # Enable basic printing support and UI.
       'enable_basic_printing%': 1,
 
@@ -819,7 +816,6 @@
 
         ['OS=="android"', {
           'enable_extensions%': 0,
-          'enable_google_now%': 0,
           'cld2_table_size%': 0,
           'enable_themes%': 0,
           'remoting%': 0,
@@ -867,7 +863,6 @@
           'configuration_policy%': 0,
           'disable_ftp_support%': 1,
           'enable_extensions%': 0,
-          'enable_google_now%': 0,
           'cld2_table_size%': 0,
           'enable_basic_printing%': 0,
           'enable_print_preview%': 0,
@@ -1221,7 +1216,6 @@
     'enable_print_preview%': '<(enable_print_preview)',
     'enable_spellcheck%': '<(enable_spellcheck)',
     'use_browser_spellchecker%': '<(use_browser_spellchecker)',
-    'enable_google_now%': '<(enable_google_now)',
     'cld_version%': '<(cld_version)',
     'cld2_table_size%': '<(cld2_table_size)',
     'enable_captive_portal_detection%': '<(enable_captive_portal_detection)',
@@ -2180,9 +2174,6 @@
       ['enable_settings_app==1', {
         'grit_defines': ['-D', 'enable_settings_app'],
       }],
-      ['enable_google_now==1', {
-        'grit_defines': ['-D', 'enable_google_now'],
-      }],
       ['use_concatenated_impulse_responses==1', {
         'grit_defines': ['-D', 'use_concatenated_impulse_responses'],
       }],
@@ -2995,9 +2986,6 @@
       ['enable_background==1', {
         'defines': ['ENABLE_BACKGROUND=1'],
       }],
-      ['enable_google_now==1', {
-        'defines': ['ENABLE_GOOGLE_NOW=1'],
-      }],
       ['enable_basic_printing==1 or enable_print_preview==1', {
         # Convenience define for ENABLE_BASIC_PRINTING || ENABLE_PRINT_PREVIEW.
         'defines': ['ENABLE_PRINTING=1'],
diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index 9cc3756..5f85713 100644
--- a/build/config/BUILD.gn
+++ b/build/config/BUILD.gn
@@ -218,9 +218,6 @@ config("feature_flags") {
   if (enable_image_loader_extension) {
     defines += [ "IMAGE_LOADER_EXTENSION=1" ]
   }
-  if (enable_google_now) {
-    defines += [ "ENABLE_GOOGLE_NOW=1" ]
-  }
   if (enable_one_click_signin) {
     defines += [ "ENABLE_ONE_CLICK_SIGNIN" ]
   }
diff --git a/build/config/features.gni b/build/config/features.gni
index 0249c44..b085ba6 100644
--- a/build/config/features.gni
+++ b/build/config/features.gni
@@ -82,8 +82,6 @@ declare_args() {
 
   enable_autofill_dialog = !is_ios
 
-  enable_google_now = !is_ios && !is_android
-
   enable_one_click_signin = is_win || is_mac || (is_linux && !is_chromeos)
 
   enable_remoting = !is_ios && !is_android && !is_chromecast && !is_headless
diff --git a/build/gypi_to_gn.py b/build/gypi_to_gn.py
index a107f94..6de1a63 100644
--- a/build/gypi_to_gn.py
+++ b/build/gypi_to_gn.py
@@ -96,10 +96,12 @@ def LoadPythonDictionary(path):
   if 'target_conditions' in file_data:
     del file_data['target_conditions']
 
-  # Strip targets in the toplevel, since some files define these and we can't
-  # slurp them in.
+  # Strip targets and includes in the toplevel, since some files define these
+  # and we can't slurp them in.
   if 'targets' in file_data:
     del file_data['targets']
+  if 'includes' in file_data:
+    del file_data['includes']
 
   return file_data
 
diff --git a/build/write_buildflag_header.py b/build/write_buildflag_header.py
new file mode 100755
index 0000000..d46cfc8
--- /dev/null
+++ b/build/write_buildflag_header.py
@@ -0,0 +1,95 @@
+#!/usr/bin/env python
+# Copyright 2015 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.
+
+# This writes headers for build flags. See buildflag_header.gni for usage of
+# this system as a whole.
+#
+# The parameters are passed in a response file so we don't have to worry
+# about command line lengths. The name of the response file is passed on the
+# command line.
+#
+# The format of the response file is:
+#    [--flags <list of one or more flag values>]
+
+import optparse
+import os
+import shlex
+import sys
+
+
+class Options:
+  def __init__(self, output, rulename, header_guard, flags):
+    self.output = output
+    self.rulename = rulename
+    self.header_guard = header_guard
+    self.flags = flags
+
+
+def GetOptions():
+  parser = optparse.OptionParser()
+  parser.add_option('--output', help="Output header name inside --gen-dir.")
+  parser.add_option('--rulename',
+                    help="Helpful name of build rule for including in the " +
+                         "comment at the top of the file.")
+  parser.add_option('--gen-dir',
+                    help="Path to root of generated file directory tree.")
+  parser.add_option('--definitions',
+                    help="Name of the response file containing the flags.")
+  cmdline_options, cmdline_flags = parser.parse_args()
+
+  # Compute header guard by replacing some chars with _ and upper-casing.
+  header_guard = cmdline_options.output.upper()
+  header_guard = \
+      header_guard.replace('/', '_').replace('\\', '_').replace('.', '_')
+  header_guard += '_'
+
+  # The actual output file is inside the gen dir.
+  output = os.path.join(cmdline_options.gen_dir, cmdline_options.output)
+
+  # Definition file in GYP is newline separated, in GN they are shell formatted.
+  # shlex can parse both of these.
+  with open(cmdline_options.definitions, 'r') as def_file:
+    defs = shlex.split(def_file.read())
+  flags_index = defs.index('--flags')
+
+  # Everything after --flags are flags. true/false are remapped to 1/0,
+  # everything else is passed through.
+  flags = []
+  for flag in defs[flags_index + 1 :]:
+    equals_index = flag.index('=')
+    key = flag[:equals_index]
+    value = flag[equals_index + 1:]
+
+    # Canonicalize and validate the value.
+    if value == 'true':
+      value = '1'
+    elif value == 'false':
+      value = '0'
+    flags.append((key, str(value)))
+
+  return Options(output=output,
+                 rulename=cmdline_options.rulename,
+                 header_guard=header_guard,
+                 flags=flags)
+
+
+def WriteHeader(options):
+  with open(options.output, 'w') as output_file:
+    output_file.write("// Generated by build/write_buildflag_header.py\n")
+    if options.rulename:
+      output_file.write('// From "' + options.rulename + '"\n')
+
+    output_file.write('\n#ifndef %s\n' % options.header_guard)
+    output_file.write('#define %s\n\n' % options.header_guard)
+    output_file.write('#include "build/buildflag.h"\n\n')
+
+    for pair in options.flags:
+      output_file.write('#define BUILDFLAG_INTERNAL_%s() (%s)\n' % pair)
+
+    output_file.write('\n#endif  // %s\n' % options.header_guard)
+
+
+options = GetOptions()
+WriteHeader(options)
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 8f19496..d09b1f2 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",
diff --git a/chrome/browser/extensions/component_loader.cc b/chrome/browser/extensions/component_loader.cc
index 1e4a738..56a5178 100644
--- a/chrome/browser/extensions/component_loader.cc
+++ b/chrome/browser/extensions/component_loader.cc
@@ -27,6 +27,7 @@
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/extensions/extension_constants.h"
+#include "chrome/common/features.h"
 #include "chrome/grit/chromium_strings.h"
 #include "chrome/grit/generated_resources.h"
 #include "components/crx_file/id_util.h"
@@ -382,7 +383,7 @@ void ComponentLoader::AddNetworkSpeechSynthesisExtension() {
 }
 
 void ComponentLoader::AddGoogleNowExtension() {
-#if defined(ENABLE_GOOGLE_NOW)
+#if BUILDFLAG(ENABLE_GOOGLE_NOW)
   const char kEnablePrefix[] = "Enable";
   const char kFieldTrialName[] = "GoogleNow";
   std::string enable_prefix(kEnablePrefix);
@@ -418,7 +419,7 @@ void ComponentLoader::AddGoogleNowExtension() {
   } else {
     DeleteData(google_now_manifest_id, root_directory);
   }
-#endif  // defined(ENABLE_GOOGLE_NOW)
+#endif  // BUILDFLAG(ENABLE_GOOGLE_NOW)
 }
 
 #if defined(OS_CHROMEOS)
diff --git a/chrome/browser/profiles/profile.cc b/chrome/browser/profiles/profile.cc
index 04d5e9f..8566442 100644
--- a/chrome/browser/profiles/profile.cc
+++ b/chrome/browser/profiles/profile.cc
@@ -12,6 +12,7 @@
 #include "chrome/browser/first_run/first_run.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/sync/profile_sync_service_factory.h"
+#include "chrome/common/features.h"
 #include "chrome/common/pref_names.h"
 #include "components/browser_sync/browser/profile_sync_service.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_prefs.h"
@@ -98,7 +99,7 @@ void Profile::RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry) {
   registry->RegisterDictionaryPref(prefs::kSafeBrowsingIncidentsSent);
   registry->RegisterBooleanPref(
       prefs::kSafeBrowsingExtendedReportingOptInAllowed, true);
-#if defined(ENABLE_GOOGLE_NOW)
+#if BUILDFLAG(ENABLE_GOOGLE_NOW)
   registry->RegisterBooleanPref(prefs::kGoogleGeolocationAccessEnabled, false);
 #endif
   // This pref is intentionally outside the above #if. That flag corresponds
diff --git a/chrome/browser/resources/BUILD.gn b/chrome/browser/resources/BUILD.gn
index a5949a2..14de709 100644
--- a/chrome/browser/resources/BUILD.gn
+++ b/chrome/browser/resources/BUILD.gn
@@ -2,10 +2,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//chrome/common/features.gni")
 import("//tools/grit/grit_rule.gni")
 
 grit("memory_internals_resources") {
   source = "memory_internals_resources.grd"
+  defines = chrome_grit_defines
   outputs = [
     "grit/memory_internals_resources.h",
     "memory_internals_resources.pak",
@@ -15,6 +17,7 @@ grit("memory_internals_resources") {
 
 grit("net_internals_resources") {
   source = "net_internals_resources.grd"
+  defines = chrome_grit_defines
   outputs = [
     "grit/net_internals_resources.h",
     "net_internals_resources.pak",
@@ -24,6 +27,7 @@ grit("net_internals_resources") {
 
 grit("invalidations_resources") {
   source = "invalidations_resources.grd"
+  defines = chrome_grit_defines
   outputs = [
     "grit/invalidations_resources.h",
     "invalidations_resources.pak",
@@ -33,6 +37,7 @@ grit("invalidations_resources") {
 
 grit("password_manager_internals_resources") {
   source = "password_manager_internals_resources.grd"
+  defines = chrome_grit_defines
   outputs = [
     "grit/password_manager_internals_resources.h",
     "password_manager_internals_resources.pak",
@@ -42,6 +47,7 @@ grit("password_manager_internals_resources") {
 
 grit("signin_internals_resources") {
   source = "signin_internals_resources.grd"
+  defines = chrome_grit_defines
   outputs = [
     "grit/signin_internals_resources.h",
     "signin_internals_resources.pak",
@@ -51,6 +57,7 @@ grit("signin_internals_resources") {
 
 grit("translate_internals_resources") {
   source = "translate_internals_resources.grd"
+  defines = chrome_grit_defines
   outputs = [
     "grit/translate_internals_resources.h",
     "translate_internals_resources.pak",
@@ -71,6 +78,7 @@ copy("extension_resource_demo") {
 if (!is_ios) {
   grit("component_extension_resources") {
     source = "component_extension_resources.grd"
+    defines = chrome_grit_defines
     outputs = [
       "grit/component_extension_resources.h",
       "grit/component_extension_resources_map.cc",
@@ -82,6 +90,7 @@ if (!is_ios) {
 
   grit("settings_resources") {
     source = "settings/settings_resources.grd"
+    defines = chrome_grit_defines
     outputs = [
       "grit/settings_resources.h",
       "grit/settings_resources_map.cc",
@@ -93,6 +102,7 @@ if (!is_ios) {
 
   grit("options_resources") {
     source = "options_resources.grd"
+    defines = chrome_grit_defines
     outputs = [
       "grit/options_resources.h",
       "options_resources.pak",
@@ -102,6 +112,7 @@ if (!is_ios) {
 
   grit("options_test_resources") {
     source = "options_test_resources.grd"
+    defines = chrome_grit_defines
     outputs = [
       "grit/options_test_resources.h",
       "options_test_resources.pak",
@@ -111,6 +122,7 @@ if (!is_ios) {
 
   grit("quota_internals_resources") {
     source = "quota_internals_resources.grd"
+    defines = chrome_grit_defines
     outputs = [
       "grit/quota_internals_resources.h",
       "quota_internals_resources.pak",
@@ -120,6 +132,7 @@ if (!is_ios) {
 
   grit("sync_file_system_internals_resources") {
     source = "sync_file_system_internals_resources.grd"
+    defines = chrome_grit_defines
     outputs = [
       "grit/sync_file_system_internals_resources.h",
       "sync_file_system_internals_resources.pak",
diff --git a/chrome/browser/ui/BUILD.gn b/chrome/browser/ui/BUILD.gn
index be6d20f..e8124cc 100644
--- a/chrome/browser/ui/BUILD.gn
+++ b/chrome/browser/ui/BUILD.gn
@@ -5,6 +5,7 @@
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
+import("//chrome/common/features.gni")
 
 gypi_values = exec_script("//build/gypi_to_gn.py",
                           [ rebase_path("../../chrome_browser_ui.gypi") ],
diff --git a/chrome/browser/ui/webui/options/content_settings_handler.cc b/chrome/browser/ui/webui/options/content_settings_handler.cc
index 10ce23a..787a884 100644
--- a/chrome/browser/ui/webui/options/content_settings_handler.cc
+++ b/chrome/browser/ui/webui/options/content_settings_handler.cc
@@ -29,6 +29,7 @@
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/extensions/manifest_handlers/app_launch_info.h"
+#include "chrome/common/features.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/generated_resources.h"
@@ -451,7 +452,7 @@ void ContentSettingsHandler::GetLocalizedValues(
     {"cookiesShowCookies", IDS_COOKIES_SHOW_COOKIES_BUTTON},
     {"flashStorageSettings", IDS_FLASH_STORAGE_SETTINGS},
     {"flashStorageUrl", IDS_FLASH_STORAGE_URL},
-#if defined(ENABLE_GOOGLE_NOW)
+#if BUILDFLAG(ENABLE_GOOGLE_NOW)
     {"googleGeolocationAccessEnable",
      IDS_GEOLOCATION_GOOGLE_ACCESS_ENABLE_CHKBOX},
 #endif
diff --git a/chrome/browser/ui/webui/options/options_ui.cc b/chrome/browser/ui/webui/options/options_ui.cc
index e69c199..56e784c 100644
--- a/chrome/browser/ui/webui/options/options_ui.cc
+++ b/chrome/browser/ui/webui/options/options_ui.cc
@@ -47,6 +47,7 @@
 #include "chrome/browser/ui/webui/options/startup_pages_handler.h"
 #include "chrome/browser/ui/webui/options/sync_setup_handler.h"
 #include "chrome/browser/ui/webui/theme_source.h"
+#include "chrome/common/features.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/generated_resources.h"
 #include "chrome/grit/locale_settings.h"
@@ -100,7 +101,7 @@
 #include "chrome/browser/ui/webui/options/certificate_manager_handler.h"
 #endif
 
-#if defined(ENABLE_GOOGLE_NOW)
+#if BUILDFLAG(ENABLE_GOOGLE_NOW)
 #include "chrome/browser/ui/webui/options/geolocation_options_handler.h"
 #endif
 
@@ -279,7 +280,7 @@ OptionsUI::OptionsUI(content::WebUI* web_ui)
   AddOptionsPageUIHandler(localized_strings, new CreateProfileHandler());
   AddOptionsPageUIHandler(localized_strings, new EasyUnlockHandler());
   AddOptionsPageUIHandler(localized_strings, new FontSettingsHandler());
-#if defined(ENABLE_GOOGLE_NOW)
+#if BUILDFLAG(ENABLE_GOOGLE_NOW)
   AddOptionsPageUIHandler(localized_strings, new GeolocationOptionsHandler());
 #endif
   AddOptionsPageUIHandler(localized_strings, new options::HelpOverlayHandler());
diff --git a/chrome/chrome.gyp b/chrome/chrome.gyp
index cfd46cc..9495002 100644
--- a/chrome/chrome.gyp
+++ b/chrome/chrome.gyp
@@ -104,6 +104,7 @@
     'chrome_browser_ui.gypi',
     'chrome_common.gypi',
     'chrome_installer_util.gypi',
+    'chrome_features.gypi',
   ],
   'conditions': [
     ['OS!="ios"', {
diff --git a/chrome/chrome_android.gypi b/chrome/chrome_android.gypi
index 9c8b394..e84068c 100644
--- a/chrome/chrome_android.gypi
+++ b/chrome/chrome_android.gypi
@@ -14,6 +14,7 @@
         'chrome.gyp:browser',
         'chrome.gyp:browser_ui',
         'chrome.gyp:child',
+        'chrome.gyp:chrome_common_features',
         'chrome.gyp:plugin',
         'chrome.gyp:renderer',
         'chrome.gyp:utility',
diff --git a/chrome/chrome_browser.gypi b/chrome/chrome_browser.gypi
index cba3bcc..6653fee 100644
--- a/chrome/chrome_browser.gypi
+++ b/chrome/chrome_browser.gypi
@@ -3066,6 +3066,7 @@
         # NOTE: New dependencies should generally be added in the OS!="ios"
         # dependencies block below, rather than here.
         'browser_ui',
+        'chrome_common_features',
         'chrome_resources.gyp:chrome_extra_resources',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
diff --git a/chrome/chrome_browser_extensions.gypi b/chrome/chrome_browser_extensions.gypi
index 8c0ca4f..7b23685 100644
--- a/chrome/chrome_browser_extensions.gypi
+++ b/chrome/chrome_browser_extensions.gypi
@@ -956,6 +956,7 @@
       # browser, then we can clean up these dependencies.
       'dependencies': [
         'browser/extensions/api/api_registration.gyp:chrome_api_registration',
+        'chrome_common_features',
         'chrome_resources.gyp:chrome_extra_resources',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
diff --git a/chrome/chrome_child.gypi b/chrome/chrome_child.gypi
index 6464a39..95298fa 100644
--- a/chrome/chrome_child.gypi
+++ b/chrome/chrome_child.gypi
@@ -9,6 +9,7 @@
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
       'dependencies': [
+        'chrome_common_features',
         '../base/base.gyp:base',
         '../content/content.gyp:content_child',
       ],
diff --git a/chrome/chrome_common.gypi b/chrome/chrome_common.gypi
index 1438853..73de6df 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',
@@ -564,6 +565,7 @@
         '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',
@@ -653,5 +655,16 @@
         '../third_party/mojo/mojo_public.gyp:mojo_cpp_bindings',
       ],
     },
+    {
+      # GN version: //chrome/common:features
+      'target_name': 'chrome_common_features',
+      'includes': [ '../build/buildflag_header.gypi' ],
+      'variables': {
+        'buildflag_header_path': 'chrome/common/features.h',
+        'buildflag_flags': [
+          'ENABLE_GOOGLE_NOW=<(enable_google_now)',
+        ],
+      },
+    },
   ],
 }
diff --git a/chrome/chrome_debugger.gypi b/chrome/chrome_debugger.gypi
index 31991c6..dae7b73 100644
--- a/chrome/chrome_debugger.gypi
+++ b/chrome/chrome_debugger.gypi
@@ -13,6 +13,7 @@
         '../base/base.gyp:base',
         '../content/content.gyp:content_browser',
         '../net/net.gyp:net',
+        'chrome_common_features',
         'browser/devtools/webrtc_device_provider_resources.gyp:webrtc_device_provider_resources',
         'browser/devtools/devtools_protocol_constants.gyp:devtools_protocol_constants',
       ],
diff --git a/chrome/chrome_exe.gypi b/chrome/chrome_exe.gypi
index f593901..286db96 100644
--- a/chrome/chrome_exe.gypi
+++ b/chrome/chrome_exe.gypi
@@ -46,7 +46,10 @@
       # GN version: //chrome:chrome_initial
       'target_name': 'chrome_initial',
       'type': 'executable',
-      'dependencies' : [ '../chrome/common_constants.gyp:version_header', ],
+      'dependencies' : [
+        '../chrome/common_constants.gyp:version_header',
+        'chrome_common_features',
+      ],
       # Name the exe chrome.exe, not chrome_initial.exe.
       'product_name': 'chrome',
       'mac_bundle': 1,
diff --git a/chrome/chrome_features.gypi b/chrome/chrome_features.gypi
new file mode 100644
index 0000000..a4d8756
--- /dev/null
+++ b/chrome/chrome_features.gypi
@@ -0,0 +1,31 @@
+# Copyright 2015 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.
+ 
+# This is the GYP equivalent of //chrome/common/features.gni.
+# Please keep in sync!
+
+{
+  'variables': {
+    'variables': {
+      # Conditional variables.
+      'conditions': [
+        ['OS=="android" or OS=="ios"', {
+          'enable_google_now%': 0,
+        }, {
+          'enable_google_now%': 1,
+        }]
+      ],
+    },
+
+    # Anything in the conditions needs to be copied to the outer scope to be
+    # accessible.
+    'enable_google_now%': '<(enable_google_now)',
+
+    # Grit defines based on the feature flags. These must be manually added to
+    # grit targets.
+    'chrome_grit_defines': [
+      '-D', 'enable_google_now=<(enable_google_now)',
+    ]
+  },
+}
diff --git a/chrome/chrome_plugin.gypi b/chrome/chrome_plugin.gypi
index 718666c..418725b 100644
--- a/chrome/chrome_plugin.gypi
+++ b/chrome/chrome_plugin.gypi
@@ -9,6 +9,7 @@
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
       'dependencies': [
+        'chrome_common_features',
         '../base/base.gyp:base',
         '../content/content.gyp:content_plugin',
         '../gin/gin.gyp:gin',
diff --git a/chrome/chrome_renderer.gypi b/chrome/chrome_renderer.gypi
index b12ac52..b8b978b 100644
--- a/chrome/chrome_renderer.gypi
+++ b/chrome/chrome_renderer.gypi
@@ -237,6 +237,7 @@
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
       'dependencies': [
+        'chrome_common_features',
         'common',
         'common_mojo_bindings',
         'chrome_resources.gyp:chrome_resources',
diff --git a/chrome/chrome_resources.gyp b/chrome/chrome_resources.gyp
index 6edb819..85116d4 100644
--- a/chrome/chrome_resources.gyp
+++ b/chrome/chrome_resources.gyp
@@ -2,8 +2,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
+  'includes': [
+    'chrome_features.gypi',
+  ],
   'variables': {
+    # Apply Chrome-specific grit settings to all grit actions in this file.
     'grit_out_dir': '<(SHARED_INTERMEDIATE_DIR)/chrome',
+    'grit_additional_defines': [ '<@(chrome_grit_defines)' ],
+
     'additional_modules_list_file': '<(SHARED_INTERMEDIATE_DIR)/chrome/browser/internal/additional_modules_list.txt',
   },
   'targets': [
diff --git a/chrome/chrome_tests.gypi b/chrome/chrome_tests.gypi
index f3a92fd9..5b6e6a9 100644
--- a/chrome/chrome_tests.gypi
+++ b/chrome/chrome_tests.gypi
@@ -1617,6 +1617,7 @@
       'type': 'executable',
       'dependencies': [
         'browser',
+        'chrome_common_features',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
         'chrome_resources.gyp:packed_extra_resources',
@@ -2111,6 +2112,7 @@
       'type': 'executable',
       'dependencies': [
         'browser',
+        'chrome_common_features',
         'chrome_resources.gyp:browser_tests_pak',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
@@ -2655,6 +2657,7 @@
       'type': 'executable',
       'dependencies': [
         'browser',
+        'chrome_common_features',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
         'chrome_resources.gyp:packed_extra_resources',
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index 1dc2c8c..f43ce67 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -1658,6 +1658,7 @@
         # NOTE: New dependencies should generally be added in the OS!="ios"
         # dependencies block below, rather than here.
         'browser',
+        'chrome_common_features',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
         'chrome_resources.gyp:theme_resources',
@@ -2212,6 +2213,7 @@
         '../ui/base/ui_base.gyp:ui_base_test_support',
         '../ui/gfx/gfx.gyp:gfx_test_support',
         '../ui/resources/ui_resources.gyp:ui_resources',
+        'chrome_common_features',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
       ],
diff --git a/chrome/chrome_utility.gypi b/chrome/chrome_utility.gypi
index d70f335..638ba4e 100644
--- a/chrome/chrome_utility.gypi
+++ b/chrome/chrome_utility.gypi
@@ -126,6 +126,7 @@
         '../third_party/libxml/libxml.gyp:libxml',
         '<(DEPTH)/chrome/chrome_resources.gyp:chrome_resources',
         '<(DEPTH)/chrome/chrome_resources.gyp:chrome_strings',
+        'chrome_common_features',
         'common',
       ],
       'include_dirs': [
diff --git a/chrome/common/BUILD.gn b/chrome/common/BUILD.gn
index bc89196..9b20bda 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",
diff --git a/chrome/common/features.gni b/chrome/common/features.gni
new file mode 100644
index 0000000..2e92745c
--- /dev/null
+++ b/chrome/common/features.gni
@@ -0,0 +1,12 @@
+# Copyright 2015 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.
+
+# This is the GN version of //chrome/chrome_features.gypi.
+# Please keep in sync!
+
+declare_args() {
+  enable_google_now = !is_ios && !is_android
+}
+
+chrome_grit_defines = [ "enable_google_now=$enable_google_now" ]
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index f3bfd8e..d546cb0 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -5,6 +5,7 @@
 #include "chrome/common/pref_names.h"
 
 #include "base/basictypes.h"
+#include "chrome/common/features.h"
 #include "chrome/common/pref_font_webkit_names.h"
 
 namespace prefs {
@@ -1557,7 +1558,7 @@ const char kGeolocationAccessToken[] = "geolocation.access_token";
 const char kGeolocationEnabled[] = "geolocation.enabled";
 #endif
 
-#if defined(ENABLE_GOOGLE_NOW)
+#if BUILDFLAG(ENABLE_GOOGLE_NOW)
 // Boolean that is true when Google services can use the user's location.
 const char kGoogleGeolocationAccessEnabled[] =
     "googlegeolocationaccess.enabled";
diff --git a/chrome/common/pref_names.h b/chrome/common/pref_names.h
index f82326b..79e1d12a 100644
--- a/chrome/common/pref_names.h
+++ b/chrome/common/pref_names.h
@@ -10,6 +10,7 @@
 #include <stddef.h>
 
 #include "build/build_config.h"
+#include "chrome/common/features.h"
 
 namespace prefs {
 
@@ -557,7 +558,7 @@ extern const char kGeolocationAccessToken[];
 extern const char kGeolocationEnabled[];
 #endif
 
-#if defined(ENABLE_GOOGLE_NOW)
+#if BUILDFLAG(ENABLE_GOOGLE_NOW)
 extern const char kGoogleGeolocationAccessEnabled[];
 #endif
 extern const char kGoogleNowLauncherEnabled[];
diff --git a/tools/grit/grit/util.py b/tools/grit/grit/util.py
index b958bc2..93dce26 100755
--- a/tools/grit/grit/util.py
+++ b/tools/grit/grit/util.py
@@ -483,7 +483,8 @@ def ParseDefine(define):
   '''Parses a define argument and returns the name and value.
 
   The format is either "NAME=VAL" or "NAME", using True as the default value.
-  Values of "1" and "0" are transformed to True and False respectively.
+  Values of "1"/"true" and "0"/"false" are transformed to True and False
+  respectively.
 
   Args:
     define: a string of the form "NAME=VAL" or "NAME".
@@ -497,8 +498,8 @@ def ParseDefine(define):
   val = True
   if len(parts) > 1:
     val = parts[1]
-  if val == "1": val = True
-  elif val == "0": val = False
+  if val == "1" or val == "true": val = True
+  elif val == "0" or val == "false": val = False
   return (name, val)
 
 
diff --git a/tools/grit/grit_rule.gni b/tools/grit/grit_rule.gni
index 083e3d9..f60d8fa 100644
--- a/tools/grit/grit_rule.gni
+++ b/tools/grit/grit_rule.gni
@@ -244,13 +244,6 @@ if (enable_settings_app) {
     "enable_settings_app",
   ]
 }
-if (enable_google_now) {
-  grit_defines += [
-    "-D",
-    "enable_google_now",
-  ]
-}
-
 if (enable_webrtc) {
   grit_defines += [
     "-D",