anchor.diff:      apt-get -qqy install google-cloud-sdk && \
       rm -rf /var/lib/apt/lists/*
   
  +### Install Docker.
  +RUN apt-get -qqy install apt-transport-https ca-certificates && \
  +    curl -sSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - && \
  +    add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" && \
  +    apt-get -qqy update && \
  +    apt-get -qqy install docker-ce && \
  +    rm -rf /var/lib/apt/lists/*
   
   ### Install Node.js and packages required by Gerrit.
   ### (see https://gerrit.googlesource.com/gerrit/+show/master/polygerrit-ui/README.md)
  
positive.code:     apt-get -qqy install google-cloud-sdk && \
      rm -rf /var/lib/apt/lists/*
  
  ### Install Node.js and packages required by Gerrit.
  ### (see https://gerrit.googlesource.com/gerrit/+show/master/polygerrit-ui/README.md)
  RUN curl -L https://deb.nodesource.com/setup_8.x | bash - && \
  
negative.code:     apt-get -qqy install google-cloud-sdk && \
      rm -rf /var/lib/apt/lists/*
  
  ### Install Docker.
  RUN apt-get -qqy install apt-transport-https ca-certificates && \
      curl -sSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - && \
      add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" && \
      apt-get -qqy update && \
      apt-get -qqy install docker-ce && \
      rm -rf /var/lib/apt/lists/*
  
  ### Install Node.js and packages required by Gerrit.
  ### (see https://gerrit.googlesource.com/gerrit/+show/master/polygerrit-ui/README.md)
  RUN curl -L https://deb.nodesource.com/setup_8.x | bash - && \
  