UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.62 Safari/537.36

Steps to reproduce the problem:
1. Try building chrome with the official guide https://chromium.googlesource.com/chromium/src/+/master/docs/windows_build_instructions.md
2. Use Windows 10 with VS2017 and Windows 10 SDK 16299.15
3. Encounter failure in runhooks after fetching chrome

What is the expected behavior?

What went wrong?
Runhooks cannot download files by looking up sha1, get the following error:
________ running 'D:\chromium\depot_tools\win_tools-2_7_6_bin\python\bin\python.exe src/third_party/depot_tools/download_from_google_storage.py --no_resume --no_auth --bucket chromium-gn -s src/buildtools/win/gn.exe.sha1' in 'D:\chromium'
0> Failed to fetch file gs://chromium-gn/68b6ac7c644184ae383a6631b8090acd8df7e905 for src/buildtools/win/gn.exe, skipping. [Err: ]
Downloading 1 files took 2.622000 second(s)
Failed to fetch file gs://chromium-gn/68b6ac7c644184ae383a6631b8090acd8df7e905 for src/buildtools/win/gn.exe. [Err: ]
Error: Command 'D:\\chromium\\depot_tools\\win_tools-2_7_6_bin\\python\\bin\\python.exe src/third_party/depot_tools/download_from_google_storage.py --no_resume --no_auth --bucket chromium-gn -s src/buildtools/win/gn.exe.sha1' returned non-zero exit status 1 in D:\chromium

Did this work before? Yes 

Chrome version: 62.0.3202.62  Channel: stable
OS Version: 10.0
Flash Version: Shockwave Flash 27.0 r0

After some dig up it appears this behavior is tied to the introduction of vpython wrapper. Since commit 23836a643f480b21e91340f2f9845619ebf6f9c4, vpython wrapper is introduced to run gsutil.py, and it doesn't work on windows environment.
I can manually bypass the vpython wrapper (by modifying src/third_party/depot_tools/gsutil.py) and it can download the files successfully. But then glclient runhooks get further error related to vpython while executing "vpython -vpython-spec src/.vpython -vpython-tool install".
After enabling vpython debug log level I can see it has something to do with encoding:
...
  File "D:\chromium\depot_tools\win_tools-2_7_6_bin\python\bin\Lib\mimetypes.py", line 297, in guess_type
    init()
  File "D:\chromium\depot_tools\win_tools-2_7_6_bin\python\bin\Lib\mimetypes.py", line 358, in init
    db.read_windows_registry()
  File "D:\chromium\depot_tools\win_tools-2_7_6_bin\python\bin\Lib\mimetypes.py", line 258, in read_windows_registry
    for subkeyname in enum_types(hkcr):
  File "D:\chromium\depot_tools\win_tools-2_7_6_bin\python\bin\Lib\mimetypes.py", line 249, in enum_types
    ctype = ctype.encode(default_encoding) # omit in 3.x!
UnicodeDecodeError: 'ascii' codec can't decode byte 0xb0 in position 1: ordinal not in range(128)
...