Treat '+' as a safe MIME type character.

util/net/http_multipart_builder.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 86 matching lines @@
 
 void AssertSafeMIMEType(const std::string& string) {
   for (size_t i = 0; i < string.length(); ++i) {
     char c = string[i];
     CHECK((c >= 'a' && c <= 'z') ||
           (c >= 'A' && c <= 'Z') ||
           (c >= '0' && c <= '9') ||
           c == '/' ||
           c == '.' ||
           c == '_' ||
+          c == '+' ||
           c == '-');
   }
 }
 
 }  // namespace
 
 HTTPMultipartBuilder::HTTPMultipartBuilder()
     : boundary_(GenerateBoundaryString()), form_data_(), file_attachments_() {
 }
 
@@ skipping 64 matching lines @@
   auto data_it = form_data_.find(key);
   if (data_it != form_data_.end())
     form_data_.erase(data_it);
 
   auto file_it = file_attachments_.find(key);
   if (file_it != file_attachments_.end())
     file_attachments_.erase(file_it);
 }
 
 }  // namespace crashpad