When building chrome/win on non-win, make sure is_win is true while running grit.

tools/grit/grit_rule.gni

 # Copyright 2014 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.
 
 # Instantiate grit. This will produce a script target to run grit, and a
 # static library that compiles the .cc files.
 #
 # Parameters
 #
 #   source (required)
@@ skipping 164 matching lines @@
 
 if (enable_image_loader_extension) {
   grit_defines += [
     "-D",
     "image_loader_extension",
   ]
 }
 
 if (is_android) {
   grit_defines += [
-    "-t",
-    "android",
     "-E",
     "ANDROID_JAVA_TAGGED_ONLY=true",
   ]
 }
 
 if (is_mac || is_ios) {
   grit_defines += [
     "-D",
     "scale_factors=2x",
   ]
 }
 
-if (is_ios) {
-  grit_defines += [
-    "-t",
-    "ios",
-  ]
+# When cross-compiling, explicitly pass the target system to grit.
+if (current_toolchain != host_toolchain) {
+  if (is_android) {
+    grit_defines += [
+      "-t",
+      "android",
+    ]

[Nico, 2016/04/04 01:36:08]

I wish `gn format` allowed `    grit_defines += [ "-t", "android" ]`, then this
file would be 88 lines shorter

+  }
+  if (is_ios) {
+    grit_defines += [
+      "-t",
+      "ios",
+    ]
+  }
+  if (is_linux) {
+    grit_defines += [
+      "-t",
+      "linux2",
+    ]
+  }
+  if (is_mac) {
+    grit_defines += [
+      "-t",
+      "darwin",
+    ]
+  }
+  if (is_win) {
+    grit_defines += [
+      "-t",
+      "win32",
+    ]
+  }
 }
 
 if (enable_extensions) {
   grit_defines += [
     "-D",
     "enable_extensions",
   ]
 }
 if (enable_media_router) {
   grit_defines += [
@@ skipping 266 matching lines @@
     if (defined(invoker.configs)) {
       configs += invoker.configs
     }
 
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
     output_name = grit_output_name
   }
 }