UserAgent: Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0

Steps to reproduce the problem:
When building chromium, it downloads the clang tolchain during the build. In situations where the build ocurs offline (no internet access once all the files are downloaded) it is not possible to build chromium using the clang toolchain.

The downloading code appears in src/tools/clang/scripts/update.py

What is the expected behavior?
An easy solution would be to download the clang toolchain before the build, and put the file in a specific directory. The download script would recognie that the toolchain is already downloaded and would not try to download it again.

I have a patch or it there: https://github.com/mildred/flatpak-electron/blob/master/electron-makefile.patch#L85-L109

What went wrong?
Build failed because of missing Internet access

Did this work before? N/A 

Chrome version: 51.0.2704.106  Channel: n/a
OS Version: 
Flash Version: