Laying the groundwork for targeting WinRT.

build/toolchain/win/BUILD.gn

Index: build/toolchain/win/BUILD.gn
diff --git a/build/toolchain/win/BUILD.gn b/build/toolchain/win/BUILD.gn
index 05406c39d42cec7a49e7b60263bb55a1a1a8d851..c7d6386758f5fde27a730f0385a6b5facc9d60a2 100644
--- a/build/toolchain/win/BUILD.gn
+++ b/build/toolchain/win/BUILD.gn
@@ -44,6 +44,7 @@ concurrent_links = exec_script("../get_concurrent_links.py", [], "value")
 
 # Parameters:
 #  current_cpu: current_cpu to pass as a build arg
+#  current_os: current_os to pass as a build arg
 #  environment: File name of environment file.
 template("msvc_toolchain") {
   if (defined(invoker.concurrent_links)) {
@@ -201,6 +202,7 @@ template("msvc_toolchain") {
     # passed to the build. They are ignored when this is the default toolchain.
     toolchain_args() {
       current_cpu = invoker.current_cpu
+      current_os = invoker.current_os
     }
   }
 }
@@ -214,6 +216,7 @@ if (current_cpu == "x86") {
     environment = "environment.x86"
 
     current_cpu = "x86"
+    current_os = "win"
   }
 }
 
@@ -222,5 +225,26 @@ if (current_cpu == "x64") {
     environment = "environment.x64"
 
     current_cpu = "x64"
+    current_os = "win"
+  }
+}
+
+if (current_os != "win") {  # WinRT toolchains
+  if (current_cpu == "x86") {

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

You can delete the two inner conditions. You can define as many toolchains as
you want. I realize the code above this does the same thing but that should be
fixed at some point (you don't have to).

+    msvc_toolchain("winrt_x86") {
+      environment = "environment.winrt_x86"
+
+      current_cpu = "x86"
+      current_os = current_os
+    }
+  }
+
+  if (current_cpu == "x64") {
+    msvc_toolchain("winrt_x64") {
+      environment = "environment.winrt_x64"
+
+      current_cpu = "x64"
+      current_os = current_os
+    }
   }
 }