New GeneratedMessage extension methods toTextFormat and writeTextFormat added to convert the message into the official protocol buffers text format. (#1080, #125)

Add well-known proto types as libraries. This change is required for protoc_plugin-25.0.0. (#1081)

Breaking: Hide PbList and PbMap constructors. It is not possible to construct these values correctly in user code, so the constructors are now private. Existing uses of PbList can be replaced by List and PbMap can be replaced by Map.

For immutable lists and maps, you can use built_value. (#1072)

Map fields now check key and value validity when adding elements. (#1065, #1076)