third_party/protobuf: update to upstream r371

third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_helpers.cc

Index: third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_helpers.cc
diff --git a/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_helpers.cc b/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_helpers.cc
index e3df88b00a25c8a8e3cbee8a9d8cbd40451c3e63..25b05a85fda183a2ac750c8782da9ab0d23df4ce 100644
--- a/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_helpers.cc
+++ b/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_helpers.cc
@@ -292,7 +292,8 @@ string DefaultValue(const FieldDescriptor* field) {
           ClassName(field->enum_type(), true),
           field->default_value_enum()->number());
     case FieldDescriptor::CPPTYPE_STRING:
-      return "\"" + CEscape(field->default_value_string()) + "\"";
+      return "\"" + EscapeTrigraphs(CEscape(field->default_value_string())) +
+             "\"";
     case FieldDescriptor::CPPTYPE_MESSAGE:
       return FieldMessageTypeName(field) + "::default_instance()";
   }
@@ -335,6 +336,11 @@ string GlobalShutdownFileName(const string& filename) {
   return "protobuf_ShutdownFile_" + FilenameIdentifier(filename);
 }
 
+// Escape C++ trigraphs by escaping question marks to \?
+string EscapeTrigraphs(const string& to_escape) {
+  return StringReplace(to_escape, "?", "\\?", true);
+}
+
 }  // namespace cpp
 }  // namespace compiler
 }  // namespace protobuf