Unbundle protobuf

[tensor5]

We disabled the use of system protobuf in Electron 1.3 due to this error:

[227/13300] ACTION Generating download_file_types.pb.
FAILED: gen/chrome/browser/resources/safe_browsing/download_file_types.pb 
cd ../../chrome; python browser/resources/safe_browsing/gen_file_type_proto.py -w -i browser/resources/safe_browsing/download_file_types.asciipb -o ../out/Release/gen/chrome/browser/resources/safe_browsing/download_file_types.pb -t linux -p ../out/Release/pyproto -p ../out/Release/pyproto/chrome/common/safe_browsing
Traceback (most recent call last):
  File "browser/resources/safe_browsing/gen_file_type_proto.py", line 200, in <module>
    sys.exit(main())
  File "browser/resources/safe_browsing/gen_file_type_proto.py", line 184, in main
    ImportProtoModules(opts.path)
  File "browser/resources/safe_browsing/gen_file_type_proto.py", line 26, in ImportProtoModules
    import download_file_types_pb2 as config_pb2
  File "../out/Release/pyproto/chrome/common/safe_browsing/download_file_types_pb2.py", line 6, in <module>
    from google.protobuf import descriptor as _descriptor
ImportError: No module named google.protobuf

We'll try and re-enable again once version 3.0.0 is out.