De-duplicate BASE_IMPLEMENTATION define in the GN build.

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
+config("base_implementation") {
+  defines = [ "BASE_IMPLEMENTATION" ]
+}
+
 source_set("base_paths") {
   sources = [
     "base_paths.cc",
     "base_paths.h",
     "base_paths_android.cc",
     "base_paths_android.h",
     "base_paths_mac.h",
     "base_paths_mac.mm",
     "base_paths_posix.cc",
     "base_paths_posix.h",
     "base_paths_win.cc",
     "base_paths_win.h",
   ]
 
   if (is_android || is_mac) {
     sources -= [ "base_paths_posix.cc" ]
   }
 
   if (is_nacl) {
     sources -= [
       "base_paths.cc",
       "base_paths_posix.cc",
     ]
   }
 
-  defines = [ "BASE_IMPLEMENTATION" ]
+  configs += [ ":base_implementation" ]
 
   deps = [
     "//base/memory",
     "//base/process",
   ]
 
   visibility = [ ":base" ]
 }
 
 component("base") {
@@ skipping 552 matching lines @@
     "win/windows_version.h",
     "win/wrapped_window_proc.cc",
     "win/wrapped_window_proc.h",
   ]
 
   sources -= [
     "sys_info_freebsd.cc",
     "sys_info_openbsd.cc",
   ]
 
-  defines = [ "BASE_IMPLEMENTATION" ]
+  configs += [ ":base_implementation" ]
 
   deps = [
     ":base_static",
     "//base/allocator:allocator_extension_thunks",
     "//base/third_party/dynamic_annotations",
     "//base/third_party/nspr",
     "//third_party/modp_b64",
   ]
 
   public_deps = [
     ":base_paths",
     "//base/debug",
     "//base/json",
     "//base/memory",
     "//base/metrics",
     "//base/process",
     "//base/trace_event",
   ]
 
   # Allow more direct string conversions on platforms with native utf8
   # strings
   if (is_mac || is_ios || is_chromeos) {
-    defines += [ "SYSTEM_NATIVE_UTF8" ]
+    defines = [ "SYSTEM_NATIVE_UTF8" ]
   }
 
   if (is_android) {
     sources -= [ "power_monitor/power_monitor_device_source_posix.cc" ]
 
     # Android uses some Linux sources, put those back.
     set_sources_assignment_filter([])
     sources += [
       "files/file_path_watcher_linux.cc",
       "posix/unix_domain_socket_linux.cc",
@@ skipping 628 matching lines @@
     "win/scoped_bstr_unittest.cc",
     "win/scoped_comptr_unittest.cc",
     "win/scoped_process_information_unittest.cc",
     "win/scoped_variant_unittest.cc",
     "win/shortcut_unittest.cc",
     "win/startup_information_unittest.cc",
     "win/win_util_unittest.cc",
     "win/wrapped_window_proc_unittest.cc",
   ]
 
-  defines = []
-
   deps = [
     ":base",
     ":i18n",
     ":message_loop_tests",
     ":prefs",
     ":prefs_test_support",
     "//base/allocator",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//base/third_party/dynamic_annotations",
     "//base/third_party/nspr",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/icu",
   ]
 
   # Allow more direct string conversions on platforms with native utf8
   # strings
   if (is_mac || is_ios || is_chromeos) {
-    defines += [ "SYSTEM_NATIVE_UTF8" ]
+    defines = [ "SYSTEM_NATIVE_UTF8" ]
   }
 
   if (is_android) {
     apk_deps = [
       ":base_java",
       ":base_java_unittest_support",
     ]
   }
 
   if (is_ios) {
@@ skipping 145 matching lines @@
 
   # GYP: //base.gyp:base_java_unittest_support
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files =
         [ "test/android/java/src/org/chromium/base/ContentUriTestUtils.java" ]
   }
 }