Deprecation warning when compiling base

[dmdashenkov]

When building the project, a warning pops up in the console:

<...>/base/base/generated/main/java/com/google/protobuf/compiler/PluginProtos.java:1206: warning: [deprecation] PARSER in FileDescriptorProto has been deprecated
                  input.readMessage(com.google.protobuf.DescriptorProtos.FileDescriptorProto.PARSER, extensionRegistry));

Note that the warning points to a generated class from the Protobuf standard library.

[alexander-yevsyukov]

We can add @Generated manually after protoc finishes. It should make Error Prone happy.
See related issues in:

• Protobuf: Generated Java source should be annotated with @Generated protocolbuffers/protobuf#2513

[alexander-yevsyukov]

No longer relevant.