using node root as --depth arg

- this was necessary in order to have intermediate make targets placed
  in the right locations
- adjusted all references to <(DEPTH) to add /chromium
- this is in tandem with a similar commit to chromium/build
  https://github.com/thlorenz/chromium-build/commit/a5758ce1858026033252fd7eb3ec9584bca5d922
- now able to build with make in Release mode on MAC
- make in Debug mode and Xcode still not working