clang/win: Fix warnings to prepare for building without -Wno-reorder.

build/secondary/testing/gtest/BUILD.gn

Index: build/secondary/testing/gtest/BUILD.gn
diff --git a/build/secondary/testing/gtest/BUILD.gn b/build/secondary/testing/gtest/BUILD.gn
index a20a09d4db6470ea5534096c1822e27a24fb3478..073faec56294fc03856b17d59c4b8745b69ded4a 100644
--- a/build/secondary/testing/gtest/BUILD.gn
+++ b/build/secondary/testing/gtest/BUILD.gn
@@ -111,6 +111,16 @@ static_library("gtest") {
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
+
+  config("gtest_warnings") {
+    if (is_win && is_clang) {
+      # The Mutex constructor initializer list in gtest-port.cc is incorrectly
+      # ordered. See
+      # https://groups.google.com/d/msg/googletestframework/S5uSV8L2TX8/U1FaTDa6J6sJ.
+      cflags = [ "-Wno-reorder" ]
+    }
+  }
+  configs += [ ":gtest_warnings" ]
 }
 
 source_set("gtest_main") {