I think we probably miss this in the layout tests as well.

You can't refer to files in depot_tools directly, so you'd have to copy cdb.exe into the build directory like we do the runtime DLLs. You might be best off modifying vs_toolchain.py:

https://cs.chromium.org/chromium/src/build/toolchain/win/BUILD.gn?l=38
https://cs.chromium.org/chromium/src/build/vs_toolchain.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6c29ace559b19a2071f4402cd201d162abd1b7ac

commit 6c29ace559b19a2071f4402cd201d162abd1b7ac
Author: jochen <jochen@chromium.org>
Date: Wed Feb 15 22:45:26 2017

Copy cdb.exe to build_root_dir so it's available to isolated tests

BUG= 690344 
R=dpranke@chromium.org,scottmg@chromium.org

Review-Url: https://codereview.chromium.org/2684033010
Cr-Commit-Position: refs/heads/master@{#450820}

[modify] https://crrev.com/6c29ace559b19a2071f4402cd201d162abd1b7ac/build/vs_toolchain.py

This will probably break some non-Google developers. I didn't have the Debuggers portion of the Windows 10 SDK installed so when I switched to DEPOT_TOOLS_WIN_TOOLCHAIN=0 my build failed because it couldn't find cdb.exe.

The fix was easy - I ran the Windows 10 SDK installer and made sure to check the Debuggers box this time. I checked the setup instructions at https://chromium.googlesource.com/chromium/src/+/master/docs/windows_build_instructions.md and they do mention this so there is nothing to do, just thought I'd mention it.

thanks for the heads-up, I added a sentence that says that cdb is required for building