Windows: Fix custom toolchain args with GN

build/config/win/visual_studio_version.gni

Index: build/config/win/visual_studio_version.gni
diff --git a/build/config/win/visual_studio_version.gni b/build/config/win/visual_studio_version.gni
index 5bfa9a76202fdb67cd32db2bcb36ec2be60bcc81..8d21080d704be72d9044cfb4d46735524f243d6b 100644
--- a/build/config/win/visual_studio_version.gni
+++ b/build/config/win/visual_studio_version.gni
@@ -12,9 +12,8 @@ declare_args() {
   # Use "2013" for Visual Studio 2013, or "2013e" for the Express version.
   visual_studio_version = ""
 
-  # Directory of the Windows driver kit. If visual_studio_path is empty, this
-  # will be auto-filled.
-  wdk_path = ""
+  # Path to Visual Studio runtime libraries.
+  visual_studio_runtime_dirs = ""
 
   # 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
@@ -28,12 +27,11 @@ if (visual_studio_path == "") {
   visual_studio_path = toolchain_data.vs_path
   windows_sdk_path = toolchain_data.sdk_path
   visual_studio_version = toolchain_data.vs_version
-  wdk_path = toolchain_data.wdk_dir
   visual_studio_runtime_dirs = toolchain_data.runtime_dirs
 } else {
   assert(visual_studio_version != "",
          "You must set the visual_studio_version if you set the path")
-  assert(wdk_path != "",
-         "You must set the wdk_path if you set the visual studio path")
-  visual_studio_runtime_dirs = []
+  assert(visual_studio_runtime_dirs != "",

[brucedawson, 2016/07/07 23:31:38]

It would be best to give an example of what to set them to. i.e.;

visual_studio_version = "2015"
visual_studio_runtime_dirs = ...

Otherwise it's difficult to figure out what is actually needed (2015? VS2015?)

+         "You must set the visual_studio_runtime_dirs if you set the visual " +
+             "studio path")
 }