Reland of Use base::flat_map for base::Value dictionary storage.

base/json/json_parser.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/json/json_parser.h"
 
 #include <cmath>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 326 matching lines @@
     ReportError(JSONReader::JSON_UNEXPECTED_TOKEN, 1);
     return nullptr;
   }
 
   StackMarker depth_check(&stack_depth_);
   if (depth_check.IsTooDeep()) {
     ReportError(JSONReader::JSON_TOO_MUCH_NESTING, 1);
     return nullptr;
   }
 
-  std::unique_ptr<DictionaryValue> dict(new DictionaryValue);
+  std::vector<Value::DictStorage::value_type> dict_storage;
 
   NextChar();
   Token token = GetNextToken();
   while (token != T_OBJECT_END) {
     if (token != T_STRING) {
       ReportError(JSONReader::JSON_UNQUOTED_DICTIONARY_KEY, 1);
       return nullptr;
     }
 
     // First consume the key.
@@ skipping 11 matching lines @@
     }
 
     // The next token is the value. Ownership transfers to |dict|.
     NextChar();
     std::unique_ptr<Value> value = ParseNextToken();
     if (!value) {
       // ReportError from deeper level.
       return nullptr;
     }
 
-    dict->SetWithoutPathExpansion(key.AsStringPiece(), std::move(value));
+    dict_storage.emplace_back(key.DestructiveAsString(), std::move(value));
 
     NextChar();
     token = GetNextToken();
     if (token == T_LIST_SEPARATOR) {
       NextChar();
       token = GetNextToken();
       if (token == T_OBJECT_END && !(options_ & JSON_ALLOW_TRAILING_COMMAS)) {
         ReportError(JSONReader::JSON_TRAILING_COMMA, 1);
         return nullptr;
       }
     } else if (token != T_OBJECT_END) {
       ReportError(JSONReader::JSON_SYNTAX_ERROR, 0);
       return nullptr;
     }
   }
 
-  return std::move(dict);
+  return MakeUnique<Value>(
+      Value::DictStorage(std::move(dict_storage), KEEP_LAST_OF_DUPES));
 }
 
 std::unique_ptr<Value> JSONParser::ConsumeList() {
   if (*pos_ != '[') {
     ReportError(JSONReader::JSON_UNEXPECTED_TOKEN, 1);
     return nullptr;
   }
 
   StackMarker depth_check(&stack_depth_);
   if (depth_check.IsTooDeep()) {
@@ skipping 422 matching lines @@
                                            const std::string& description) {
   if (line || column) {
     return StringPrintf("Line: %i, column: %i, %s",
         line, column, description.c_str());
   }
   return description;
 }
 
 }  // namespace internal
 }  // namespace base