Version: master
OS: Windows 10 1607

What steps will reproduce the problem?
(1) Setup a Chromium build on Windows 10 following https://chromium.googlesource.com/chromium/src/+/master/docs/windows_build_instructions.md
(2) ninja -C out/Default

What is the expected output?
A successful build.

What do you see instead?
FAILED: cdb/cdb.exe cdb/dbgeng.dll cdb/dbghelp.dll cdb/dbgmodel.dll cdb/winext/ext.dll cdb/winext/uext.dll cdb/winxp/exts.dll cdb/winxp/ntsdexts.dll
C:/Users/pwnall/depot_tools/python276_bin/python.exe ../../build/win/copy_cdb_to_output.py cdb x64
Traceback (most recent call last):
  File "../../build/win/copy_cdb_to_output.py", line 104, in <module>
    sys.exit(main())
  File "../../build/win/copy_cdb_to_output.py", line 100, in main
    return _CopyCDBToOutput(sys.argv[1], sys.argv[2])
  File "../../build/win/copy_cdb_to_output.py", line 84, in _CopyCDBToOutput
    _CopyImpl('cdb.exe', output_dir, src_dir)
  File "../../build/win/copy_cdb_to_output.py", line 43, in _CopyImpl
    shutil.copy(source, target)
  File "C:\Users\pwnall\depot_tools\python276_bin\lib\shutil.py", line 119, in copy
    copyfile(src, dst)
  File "C:\Users\pwnall\depot_tools\python276_bin\lib\shutil.py", line 82, in copyfile
    with open(src, 'rb') as fsrc:
IOError: [Errno 2] No such file or directory: 'C:\\Program Files (x86)\\Windows Kits\\10\\Debuggers\\x64\\cdb.exe'

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I will upload a CL that modifies the build instructions.