What steps will reproduce the problem?
(0) set DEPOT_TOOLS_WIN_TOOLCHAIN= 
   e.g. use default, e.g. =1, e.g. obtain toolchain through depot_tools

(1) Put win toolchain hash in build/vs_toolchain.py that I have available

(2) Run gn gen --args=is_debug=false out/Release

What is the expected result?

gn succeed

What happens instead?
ERROR at dynamically parsed input that //build/config/win/visual_studio_version.gni:28:7 loaded :1:39: Invalid token.
Windows toolchain out of date or doesn't exist, updating (Pro)...
                                      ^
Strings are delimited by " characters, not apostrophes.
See //build/toolchain/win/BUILD.gn:8:1: whence it was imported.
import("//build/config/win/visual_studio_version.gni")
^----------------------------------------------------
See //BUILD.gn:5:1: which caused the file to be included.
group("root") {
^--------------