SearchSuggestionParser: Use a StringPiece instead of modifying a string.

components/omnibox/search_suggestion_parser.cc

 // Copyright 2014 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 "components/omnibox/search_suggestion_parser.h"
 
 #include "base/i18n/icu_string_conversions.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/json/json_writer.h"
 #include "base/logging.h"
@@ skipping 325 matching lines @@
                                 base::OnStringConversionError::FAIL,
                                 &data_16))
         json_data = base::UTF16ToUTF8(data_16);
     }
   }
   return json_data;
 }
 
 // static
 scoped_ptr<base::Value> SearchSuggestionParser::DeserializeJsonData(
-    std::string json_data) {
+    base::StringPiece json_data) {
   // The JSON response should be an array.
   for (size_t response_start_index = json_data.find("["), i = 0;
-       response_start_index != std::string::npos && i < 5;
+       response_start_index != base::StringPiece::npos && i < 5;
        response_start_index = json_data.find("[", 1), i++) {
     // Remove any XSSI guards to allow for JSON parsing.
-    if (response_start_index > 0)
-      json_data.erase(0, response_start_index);
+    json_data.remove_prefix(response_start_index);
 
     JSONStringValueSerializer deserializer(json_data);
     deserializer.set_allow_trailing_comma(true);
     int error_code = 0;
     scoped_ptr<base::Value> data(deserializer.Deserialize(&error_code, NULL));
     if (error_code == 0)
       return data.Pass();
   }
   return scoped_ptr<base::Value>();
 }
@@ skipping 158 matching lines @@
           base::CollapseWhitespace(suggestion, false), match_type,
           base::CollapseWhitespace(match_contents, false),
           match_contents_prefix, annotation, answer_contents, answer_type_str,
           answer.Pass(), suggest_query_params, deletion_url, is_keyword_result,
           relevance, relevances != NULL, should_prefetch, trimmed_input));
     }
   }
   results->relevances_from_server = relevances != NULL;
   return true;
 }