Update Chomium's build files to work w/ latest GN binaries.

build/compiled_action.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.
 
 # This file introduces two related templates that act like action and
 # action_foreach but instead of running a Python script, it will compile a
 # given tool in the host toolchain and run that (either once or over the list
 # of inputs, depending on the variant).
 #
 # Parameters
@@ skipping 48 matching lines @@
 #   if (host_toolchain == current_toolchain) {
 #     executable("mytool") {
 #       ...
 #     }
 #   }
 # The if statement around the executable is optional. That says "I only care
 # about this target in the host toolchain". Usually this is what you want, and
 # saves unnecessarily compiling your tool for the target platform. But if you
 # need a target build of your tool as well, just leave off the if statement.
 
-if (build_os == "win") {
+if (host_os == "win") {
   _host_executable_suffix = ".exe"
 } else {
   _host_executable_suffix = ""
 }
 
 template("compiled_action") {
   assert(defined(invoker.tool), "tool must be defined for $target_name")
   assert(defined(invoker.outputs), "outputs must be defined for $target_name")
   assert(defined(invoker.args), "args must be defined for $target_name")
 
@@ skipping 84 matching lines @@
     ]
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
 
     # The script takes as arguments the binary to run, and then the arguments
     # to pass it.
     args = [ rebase_path(host_executable, root_build_dir) ] + invoker.args
   }
 }