Test sources for gn-build originally based from timniederhausen's testsrc

1. git clone --depth 1 --single-branch -b ns https://github.com/dyu/gn-build

2. On linux:

   gn gen gn-out --args='gcc_cc="gcc" gcc_cxx="g++" symbol_level=0 is_debug=false is_clang=false is_official_build=true'

   On windows:

   gn gen gn-out --args="visual_studio_path=\"C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\" visual_studio_version=\"2015\" symbol_level=0 is_debug=false is_clang=false is_official_build=true"

3. ninja -C gn-out