gn win: Add system include directories to midl template

Otherwise, midl.exe will fail to find standard .idls, e.g.:

midl : command line error MIDL1001 : cannot open input file objidl.idl

R=brettw@chromium.org
BUG=354261

Review URL: https://codereview.chromium.org/423263002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@286437 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

config/win/BUILD.gn

@@ -20,23 +20,9 @@ config("sdk") {
     "WINVER=0x0602",
   ]
 
-  # The Windows SDK include directories must be first. They both have a sal.h,
-  # and the SDK one is newer and the SDK uses some newer features from it not
-  # present in the Visual Studio one.
-  include_dirs = [
-    "$windows_sdk_path\Include\shared",
-    "$windows_sdk_path\Include\um",
-    "$windows_sdk_path\Include\winrt",
-    "$visual_studio_path\VC\include",
-    "$visual_studio_path\VC\atlmfc\include",
-  ]
+  include_dirs = system_include_dirs
 
   if (is_visual_studio_express) {
-    include_dirs += [
-      "$wdk_path/inc/atl71",
-      "$wdk_path/inc/mfc42",
-    ]
-
     # https://code.google.com/p/chromium/issues/detail?id=372451#c20
     # Warning 4702 ("Unreachable code") should be re-enabled once Express users
     # are updated to VS2013 Update 2.

config/win/visual_studio_version.gni

@@ -20,6 +20,11 @@ declare_args() {
   # This value is the default location, override if you have a different
   # installation location.
   windows_sdk_path = "C:\Program Files (x86)\Windows Kits\8.0"
+
+  # The list of include directories that are treated as "system" include
+  # directories. TODO(scottmg): These are incorrectly put on the command line
+  # in GN, they should really be stored into %INCLUDE%.
+  system_include_dirs = []
 }
 
 if (visual_studio_path == "") {
@@ -38,3 +43,22 @@ if (visual_studio_path == "") {
 
 # Set when using the "Express" version of a Visual Studio version we support.
 is_visual_studio_express = (visual_studio_version == "2013e")
+
+
+# The Windows SDK include directories must be first. They both have a sal.h,
+# and the SDK one is newer and the SDK uses some newer features from it not
+# present in the Visual Studio one.
+system_include_dirs = [
+  "$windows_sdk_path\Include\shared",
+  "$windows_sdk_path\Include\um",
+  "$windows_sdk_path\Include\winrt",
+  "$visual_studio_path\VC\include",
+  "$visual_studio_path\VC\atlmfc\include",
+]
+
+if (is_visual_studio_express) {
+  system_include_dirs += [
+    "$wdk_path/inc/atl71",
+    "$wdk_path/inc/mfc42",
+  ]
+}

toolchain/win/midl.gni

@@ -4,6 +4,8 @@
 
 assert(is_win)
 
+import("//build/config/win/visual_studio_version.gni")
+
 # This template defines a rule to invoke the MS IDL compiler.
 #
 # Parameters
@@ -77,6 +79,10 @@ template("midl") {
       "/env", idl_target_platform,
       "/Oicf",
     ]
+
+    foreach(include, system_include_dirs) {
+      args += [ "/I", include ]
+    }
   }
 
   source_set(target_name) {