New build flag system, convert Google Now flag

build/buildflag_header.gypi

+# 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)',
+      ],
+    }
+  ],
+}