Use depot_tools toolchain, remove now unneeded code, fix not including path to win sdk tools

build/config/win/visual_studio_version.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.
 
 declare_args() {
-  # Version of Visual Studio to use.
-  #
-  # Possible values:
-  #  - "auto"
-  #  - "2010"
-  #  - "2010e"
-  #  - "2012"
-  #  - "2012e"
-  #  - "2013"
-  #  - "2013e"
-  #
-  # The "e" variants denote "Express". The default, "auto" will find the
-  # preferred one of all Visual Studios installed on the current system.
-  visual_studio_version = "auto"
+  # Path to Visual Studio. In Chrome, this is the depot_tools toolchain.

[brettw, 2014/03/20 05:46:22]

Can you document that empty means to use the default.

[scottmg, 2014/03/20 16:01:18]

Done.

+  visual_studio_path = ""
 
-  # The path to use as the root of a Visual Studio install. If nonempty,
-  # this path will be used instead of any autodetected install locations,
-  # which allows you to have the Visual Studio files in a directory without
-  # actually "installing" it.
-  #
-  # When empty, we will autodetect the best Visual Studio path to use. The
-  # autodetected one is usually something like
-  # "C:\Program Files (x86)\Microsoft Visual Studio 10.0".
-  visual_studio_path = ""
+  # Full path to the Windows SDK, not including a backslash at the end.
+  # 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"
 }
 
 if (visual_studio_path == "") {
-  visual_studio_path = exec_script("get_visual_studio_path.py",
-                                   [ visual_studio_version ], "value")
+  toolchain_data = 
+      exec_script("../../vs_toolchain.py", [ "get_toolchain_dir" ], "value")
+  visual_studio_path = toolchain_data[0]
+  windows_sdk_path = toolchain_data[1]
 }