third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/src/google/protobuf/util/field_mask_util.h

Index: third_party/protobuf/src/google/protobuf/util/field_mask_util.h
diff --git a/third_party/protobuf/src/google/protobuf/util/field_mask_util.h b/third_party/protobuf/src/google/protobuf/util/field_mask_util.h
index 644161b940190735e6956c0cedbf1c3aff63c933..396c9aea599f3897b8a3a954c8ae00277ac691c5 100644
--- a/third_party/protobuf/src/google/protobuf/util/field_mask_util.h
+++ b/third_party/protobuf/src/google/protobuf/util/field_mask_util.h
@@ -28,6 +28,8 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+// Defines utilities for the FieldMask well known type.
+
 #ifndef GOOGLE_PROTOBUF_UTIL_FIELD_MASK_UTIL_H__
 #define GOOGLE_PROTOBUF_UTIL_FIELD_MASK_UTIL_H__
 
@@ -107,10 +109,16 @@ class LIBPROTOBUF_EXPORT FieldMaskUtil {
   static bool IsPathInFieldMask(StringPiece path, const FieldMask& mask);
 
   class MergeOptions;
-  // Merges fields specified in a FieldMask into another message.
+  // Merges fields specified in a FieldMask into another message. See the
+  // comments in MergeOptions regarding compatibility with
+  // google/protobuf/field_mask.proto
   static void MergeMessageTo(const Message& source, const FieldMask& mask,
                              const MergeOptions& options, Message* destination);
 
+  // Removes from 'message' any field that is not represented in the given
+  // FieldMask. If the FieldMask is empty, does nothing.
+  static void TrimMessage(const FieldMask& mask, Message* message);
+
  private:
   friend class SnakeCaseCamelCaseTest;
   // Converts a field name from snake_case to camelCase:
@@ -148,6 +156,10 @@ class LIBPROTOBUF_EXPORT FieldMaskUtil {
                                                FieldMask* out);
 };
 
+// Note that for compatibility with the defined behaviour for FieldMask in
+// google/protobuf/field_mask.proto, set replace_message_fields and
+// replace_repeated_fields to 'true'. The default options are not compatible
+// with google/protobuf/field_mask.proto.
 class LIBPROTOBUF_EXPORT FieldMaskUtil::MergeOptions {
  public:
   MergeOptions()