Use split_static_library in GN build.

build/config/BUILDCONFIG.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.
 
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
@@ skipping 584 matching lines @@
 # Source set defaults (also for components in non-component mode).
 set_defaults("source_set") {
   configs = _native_compiler_configs
 }
 if (!is_component_build) {
   set_defaults("component") {
     configs = _native_compiler_configs
   }
 }
 
+# TODO(brettw) move to //build/split_static_library.gni when set_defaults can
+# be practically implemented outside of this file.
+set_defaults("split_static_library") {
+  configs = _native_compiler_configs
+}
+
 # Test defaults.
 set_defaults("test") {
   if (is_android) {
     configs = _shared_library_configs
   } else {
     configs = _executable_configs
   }
 }
 
 # ==============================================================================
@@ skipping 41 matching lines @@
     forward_variables_from(invoker, "*", [ "visibility" ])
 
     # All shared libraries must have the sanitizer deps to properly link in
     # asan mode (this target will be empty in other cases).
     if (!defined(deps)) {
       deps = []
     }
     deps += [ "//build/config/sanitizers:deps" ]
   }
 }