Handle unpatched VS xtree header

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.
 
 # =============================================================================
 # BUILD FLAGS
 # =============================================================================
 #
 # This block lists input arguments to the build, along with their default
 # values. GN requires listing them explicitly so it can validate input and have
@@ skipping 338 matching lines @@
   "//build/config/compiler:compiler_arm_fpu",
   "//build/config/compiler:chromium_code",
   "//build/config/compiler:default_include_dirs",
   "//build/config/compiler:default_warnings",
   "//build/config/compiler:no_rtti",
   "//build/config/compiler:runtime_library",
 ]
 if (is_win) {
   _native_compiler_configs += [
     "//build/config/win:lean_and_mean",
+    "//build/config/win:msvs_xtree_unreachable_code",

[brettw, 2015/02/27 22:43:24]

We only need to add stuff to this list of targets need to opt-out of that
warning specifically. In this case, it looks like we want everybody to get this
flag.

We can instead add cflags = [ "/wd4702" ] to the
//build/config/compiler:default_warnings config to avoid this.

Also, since we don't need to share the xtree value with any other .gn files, we
can move the exec_script call to that file in an "if (is_win)" block.

Last, do we need to set this value from "gn args"? I can't think of any reason
why I would want to do this. In this case, we shouldn't put the variable in the
declare_args block and just use a normal file-local variable.

     "//build/config/win:nominmax",
     "//build/config/win:sdk",
     "//build/config/win:unicode",
     "//build/config/win:winver",
   ]
 }
 if (is_posix) {
   _native_compiler_configs += [
     "//build/config/gcc:no_exceptions",
     "//build/config/gcc:symbol_visibility_hidden",
@@ skipping 387 matching lines @@
       }
       if (defined(invoker.testonly)) {
         testonly = invoker.testonly
       }
       if (defined(invoker.visibility)) {
         visibility = invoker.visibility
       }
     }
   }
 }