Update //third_party/protobuf to version 3.

third_party/protobuf/cmake/libprotobuf.cmake

+set(libprotobuf_files
+  ${protobuf_source_dir}/src/google/protobuf/any.cc
+  ${protobuf_source_dir}/src/google/protobuf/any.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/api.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/compiler/importer.cc
+  ${protobuf_source_dir}/src/google/protobuf/compiler/parser.cc
+  ${protobuf_source_dir}/src/google/protobuf/descriptor.cc
+  ${protobuf_source_dir}/src/google/protobuf/descriptor.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/descriptor_database.cc
+  ${protobuf_source_dir}/src/google/protobuf/duration.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/dynamic_message.cc
+  ${protobuf_source_dir}/src/google/protobuf/empty.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/extension_set_heavy.cc
+  ${protobuf_source_dir}/src/google/protobuf/field_mask.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/generated_message_reflection.cc
+  ${protobuf_source_dir}/src/google/protobuf/io/gzip_stream.cc
+  ${protobuf_source_dir}/src/google/protobuf/io/printer.cc
+  ${protobuf_source_dir}/src/google/protobuf/io/strtod.cc
+  ${protobuf_source_dir}/src/google/protobuf/io/tokenizer.cc
+  ${protobuf_source_dir}/src/google/protobuf/io/zero_copy_stream_impl.cc
+  ${protobuf_source_dir}/src/google/protobuf/map_field.cc
+  ${protobuf_source_dir}/src/google/protobuf/message.cc
+  ${protobuf_source_dir}/src/google/protobuf/reflection_ops.cc
+  ${protobuf_source_dir}/src/google/protobuf/service.cc
+  ${protobuf_source_dir}/src/google/protobuf/source_context.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/struct.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/stubs/mathlimits.cc
+  ${protobuf_source_dir}/src/google/protobuf/stubs/substitute.cc
+  ${protobuf_source_dir}/src/google/protobuf/text_format.cc
+  ${protobuf_source_dir}/src/google/protobuf/timestamp.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/type.pb.cc
+  ${protobuf_source_dir}/src/google/protobuf/unknown_field_set.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/field_comparator.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/field_mask_util.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/datapiece.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/default_value_objectwriter.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/error_listener.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/field_mask_utility.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/json_escaping.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/json_objectwriter.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/json_stream_parser.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/object_writer.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/proto_writer.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/protostream_objectsource.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/protostream_objectwriter.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/type_info.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/type_info_test_helper.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/internal/utility.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/json_util.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/message_differencer.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/time_util.cc
+  ${protobuf_source_dir}/src/google/protobuf/util/type_resolver_util.cc
+  ${protobuf_source_dir}/src/google/protobuf/wire_format.cc
+  ${protobuf_source_dir}/src/google/protobuf/wrappers.pb.cc
+)
+
+add_library(libprotobuf ${protobuf_SHARED_OR_STATIC}
+  ${libprotobuf_lite_files} ${libprotobuf_files})
+target_link_libraries(libprotobuf ${CMAKE_THREAD_LIBS_INIT} ${ZLIB_LIBRARIES})
+target_include_directories(libprotobuf PUBLIC ${protobuf_source_dir}/src)
+if(MSVC AND protobuf_BUILD_SHARED_LIBS)
+  target_compile_definitions(libprotobuf
+    PUBLIC  PROTOBUF_USE_DLLS
+    PRIVATE LIBPROTOBUF_EXPORTS)
+endif()
+set_target_properties(libprotobuf PROPERTIES
+    OUTPUT_NAME ${LIB_PREFIX}protobuf
+    DEBUG_POSTFIX "${protobuf_DEBUG_POSTFIX}")