Laying the groundwork for targeting WinRT.

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 660d1f39ec85a1e06ff29ef0fdf53c9a5c9c7548..1b0bc02cd9362b4dd706719af85d829a9036c4d9 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -153,7 +153,8 @@ declare_args() {
 # aix or one of the BSDs. If you need to check these, just check the
 # current_os value directly.
 
-if (current_os == "win") {
+if (current_os == "win" || current_os == "winrt_81" ||
+    current_os == "winrt_81_phone" || current_os == "winrt_10") {
   is_android = false
   is_chromeos = false
   is_ios = false
@@ -373,6 +374,10 @@ if (is_win) {
     "//build/config/win:winver",
   ]
 }
+if (current_os == "winrt_81" || current_os == "winrt_81_phone" ||
+    current_os == "winrt_10") {
+  _native_compiler_configs += [ "//build/config/win:target_winrt" ]
+}
 if (is_posix) {
   _native_compiler_configs += [
     "//build/config/gcc:no_exceptions",
@@ -529,7 +534,16 @@ if (is_win) {
   } else if (current_cpu == "x86") {
     host_toolchain = "//build/toolchain/win:32"
   }
-  set_default_toolchain("$host_toolchain")
+
+  if (current_os == "win") {
+    set_default_toolchain("$host_toolchain")
+  } else {  # WinRT variants

[brettw, 2015/07/22 20:29:19]

Just eliminate this and make the whole thing one big if/else block.

+    if (current_cpu == "x64") {
+      set_default_toolchain("//build/toolchain/win:winrt_x64")
+    } else if (current_cpu == "x86") {
+      set_default_toolchain("//build/toolchain/win:winrt_x86")
+    }
+  }
 } else if (is_android) {
   if (host_os == "linux") {
     # Use clang for the x86/64 Linux host builds.