Convert GN single-item list concat to use lists.

tools/gn/secondary/third_party/snappy/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.
 
 config("snappy_config") {
   include_dirs = [
     "src",
   ]
 
   # These OS-specific generated headers were made by running the configure
   # script offline.
   if (is_win) {
-    include_dirs += "win32"
+    include_dirs += [ "win32" ]
   } else if (is_mac) {
-    include_dirs += "mac"
+    include_dirs += [ "mac" ]
   } else {
-    include_dirs += "linux"
+    include_dirs += [ "linux" ]
   }
 }
 
 static_library("snappy") {
   sources = [
     "src/snappy-internal.h",
     "src/snappy-sinksource.cc",
     "src/snappy-sinksource.h",
     "src/snappy-stubs-internal.cc",
     "src/snappy-stubs-internal.h",
     "src/snappy.cc",
     "src/snappy.h",
   ]
 
-  configs -= "//build/config/compiler:chromium_code"
-  configs += "//build/config/compiler:no_chromium_code"
+  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs += [ "//build/config/compiler:no_chromium_code" ]
   direct_dependent_configs = [ ":snappy_config" ]
 
   #['OS=="win"', {
   #          # Signed/unsigned comparison
   #          'msvs_disabled_warnings': [
   #            # https://code.google.com/p/snappy/issues/detail?id=71
   #            4018,
   #            # https://code.google.com/p/snappy/issues/detail?id=75
   #            4267,
   #          ],
   #        }],
   #      ['clang == 1', {
   #          # snappy-stubs-internal.h unapologetically has: using namespace std
   #          # https://code.google.com/p/snappy/issues/detail?id=70
   #          'xcode_settings': {
   #            'WARNING_CFLAGS!': [ '-Wheader-hygiene' ],
   #          },
   #          'cflags!': [ '-Wheader-hygiene' ],
   #        }],
   #    ],
 }
 
 test("snappy_unittest") {
   sources = [
     "src/snappy-test.cc",
     "src/snappy-test.h",
     "src/snappy_unittest.cc",
   ]
 
-  configs -= "//build/config/compiler:chromium_code"
-  configs += "//build/config/compiler:no_chromium_code"
+  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs += [ "//build/config/compiler:no_chromium_code" ]
 
   deps = [
     ":snappy",
     "//base",
     "//testing/gtest",
     "//third_party/zlib",
   ]
 }