The suggested way to build it is:
1. git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
2. export PATH="$PATH:/path/to/depot_tools"
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3. mkdir ~/chromium && cd ~/chromium
4. fetch --nohooks chromium
5. cd src
6. gclient runhooks
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7. git remote add lp-origin
8. git remote add lp-origin lp:ozone-mir
9. git fetch lp-origin
10. git checkout lp-origin/ozone-mir
11. gn args out/Ozone --args="use_ozone=true enable_package_mash_services=true treat_warnings_as_errors=false use_sysroot=false is_component_build=false"
12. ninja -C out/Ozone mash mash:all chrome