third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_field.h

Index: third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_field.h
diff --git a/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_field.h b/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_field.h
index 3b01252780da26393e0056c802f068bea1b7f044..fdd338a65a968e1b13336d49c2c7471be9ab1761 100644
--- a/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_field.h
+++ b/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_field.h
@@ -136,6 +136,13 @@ class FieldGenerator {
   // GenerateMergeFrom method.
   virtual void GenerateMergingCode(io::Printer* printer) const = 0;
 
+  // The same, but the generated code may or may not check the possibility that
+  // the two objects being merged have the same address.  To be safe, callers
+  // should avoid calling this unless they know the objects are different.
+  virtual void GenerateUnsafeMergingCode(io::Printer* printer) const {
+    GenerateMergingCode(printer);
+  }
+
   // Generate lines of code (statements, not declarations) which swaps
   // this field and the corresponding field of another message, which
   // is stored in the generated code variable "other". This is used to