Add script for downloading *.proto files from protobuf/googleapis repositories & running protoc compiler
Add script for downloading *.proto files from protobuf/googleapis repositories & running protoc compiler

R=vegorov@google.com

Review-Url: https://codereview.chromium.org//2719943002 .

exitlive/appengine,exitlive/appengine,dart-lang/appengine,exitlive/appengine,dart-lang/appengine