old_contents: {
    "targets": [
      {
        "target_name": "bindings",
        "include_dirs": [ "/usr/local/include/raptor2" ],
        "sources": [ "src/bindings.cc", "src/parser.cc", "src/serializer.cc", "src/statement.cc" ],
        "link_settings": {
          "libraries": [ "-lraptor2" ]
        }
      }
    ]
  }
  
new_contents: { "targets": [ {
        "target_name": "bindings",
        "variables": {
          "raptor_prefix": "/usr/local"
        },
        "include_dirs": [
          "<(raptor_prefix)/include/raptor2"
        ],
        "sources": [
          "src/bindings.cc",
          "src/parser.cc",
          "src/serializer.cc",
          "src/statement.cc"
        ],
        "link_settings": {
          "libraries": [ "-lraptor2" ]
        }
      }
    ]
  }
  
subject: Add rapor_prefix variable.