Allow multiple set_default calls in GN.

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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 90 matching lines @@
     if (is_android || is_mac || is_ios) {
       sources -= [ "base_paths_posix.cc" ]
     }
 
     configs += [ ":base_implementation" ]
 
     visibility = [ ":base" ]
   }
 }
 
-config("android_system_libs") {
-  libs = [ "log" ]  # Used by logging.cc.
+if (is_android) {
+  config("android_system_libs") {
+    libs = [ "log" ]  # Used by logging.cc.
+  }
 }
 
 # Base and everything it depends on should be a static library rather than
 # a source set. Base is more of a "library" in the classic sense in that many
 # small parts of it are used in many different contexts. This combined with a
 # few static initializers floating around means that dead code stripping
 # still leaves a lot of code behind that isn't always used. For example, this
 # saves more than 40K for a smaller target like chrome_elf.
 #
 # Use static libraries for the helper stuff as well like //base/debug since
@@ skipping 2305 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" ]
   }
 }