Fix few trivial Coverity issues, mainly PASS_BY_VALUE.

base/tracked_objects.cc

 // Copyright (c) 2006-2008 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/tracked_objects.h"
 
 #include <math.h>
 
 #include "base/message_loop.h"
 #include "base/string_util.h"
@@ skipping 747 matching lines @@
 
       default:
         break;
     }
   }
   if (tiebreaker_ && !use_tiebreaker_for_sort_only_)
     return tiebreaker_->Acceptable(sample);
   return true;
 }
 
-void Comparator::SetTiebreaker(Selector selector, const std::string required) {
+void Comparator::SetTiebreaker(Selector selector, const std::string& required) {
   if (selector == selector_ || NIL == selector)
     return;
   combined_selectors_ |= selector;
   if (NIL == selector_) {
     selector_ = selector;
     if (required.size())
       required_ = required;
     return;
   }
   if (tiebreaker_) {
@@ skipping 18 matching lines @@
     return;
   if (!tiebreaker_) {
     use_tiebreaker_for_sort_only_ = true;
     tiebreaker_ = new Comparator;
     tiebreaker_->SetTiebreaker(selector, "");
   } else {
     tiebreaker_->SetSubgroupTiebreaker(selector);
   }
 }
 
-void Comparator::ParseKeyphrase(const std::string key_phrase) {
+void Comparator::ParseKeyphrase(const std::string& key_phrase) {
   static std::map<const std::string, Selector> key_map;
   static bool initialized = false;
   if (!initialized) {
     initialized = true;
     key_map["count"]    = COUNT;
     key_map["duration"] = AVERAGE_DURATION;
     key_map["birth"]    = BIRTH_THREAD;
     key_map["death"]    = DEATH_THREAD;
     key_map["file"]     = BIRTH_FILE;
     key_map["function"] = BIRTH_FUNCTION;
     key_map["line"]     = BIRTH_LINE;
   }
 
   std::string required;
   size_t equal_offset = key_phrase.find('=', 0);
   if (key_phrase.npos != equal_offset)
     required = key_phrase.substr(equal_offset + 1, key_phrase.npos);
   std::string keyword(key_phrase.substr(0, equal_offset));
   keyword = StringToLowerASCII(keyword);
   if (key_map.end() == key_map.find(keyword))
     return;
   SetTiebreaker(key_map[keyword], required);
 }
 
-bool Comparator::ParseQuery(const std::string query) {
+bool Comparator::ParseQuery(const std::string& query) {
   for (size_t i = 0; i < query.size();) {
     size_t slash_offset = query.find('/', i);
     ParseKeyphrase(query.substr(i, slash_offset - i));
     if (query.npos == slash_offset)
       break;
     i = slash_offset + 1;
   }
 
   // Select subgroup ordering (if we want to display the subgroup)
   SetSubgroupTiebreaker(COUNT);
@@ skipping 55 matching lines @@
                   (combined_selectors_ & BIRTH_THREAD) ? "*" :
                     sample.birth().birth_thread()->ThreadName().c_str(),
                   (combined_selectors_ & DEATH_THREAD) ? "*" :
                     sample.DeathThreadName().c_str());
   sample.birth().location().Write(!(combined_selectors_ & BIRTH_FILE),
                                   !(combined_selectors_ & BIRTH_FUNCTION),
                                   output);
 }
 
 }  // namespace tracked_objects