Fix few trivial Coverity issues, mainly PASS_BY_VALUE.

base/tracked_objects.h

 // 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.
 
 #ifndef BASE_TRACKED_OBJECTS_H_
 #define BASE_TRACKED_OBJECTS_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 237 matching lines @@
 
   // Check to see if the items are sort equivalents (should be aggregated).
   bool Equivalent(const Snapshot& left, const Snapshot& right) const;
 
   // Check to see if all required fields are present in the given sample.
   bool Acceptable(const Snapshot& sample) const;
 
   // A comparator can be refined by specifying what to do if the selected basis
   // for comparison is insufficient to establish an ordering.  This call adds
   // the indicated attribute as the new "least significant" basis of comparison.
-  void SetTiebreaker(Selector selector, const std::string required);
+  void SetTiebreaker(Selector selector, const std::string& required);
 
   // Indicate if this instance is set up to sort by the given Selector, thereby
   // putting that information in the SortGrouping, so it is not needed in each
   // printed line.
   bool IsGroupedBy(Selector selector) const;
 
   // Using the tiebreakers as set above, we mostly get an ordering, which
   // equivalent groups.  If those groups are displayed (rather than just being
   // aggregated, then the following is used to order them (within the group).
   void SetSubgroupTiebreaker(Selector selector);
 
   // Translate a keyword and restriction in URL path to a selector for sorting.
-  void ParseKeyphrase(const std::string key_phrase);
+  void ParseKeyphrase(const std::string& key_phrase);
 
   // Parse a query in an about:objects URL to decide on sort ordering.
-  bool ParseQuery(const std::string query);
+  bool ParseQuery(const std::string& query);
 
   // Output a header line that can be used to indicated what items will be
   // collected in the group.  It lists all (potentially) tested attributes and
   // their values (in the sample item).
   bool WriteSortGrouping(const Snapshot& sample, std::string* output) const;
 
   // Output a sample, with SortGroup details not displayed.
   void WriteSnapshot(const Snapshot& sample, std::string* output) const;
 
  private:
@@ skipping 220 matching lines @@
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(AutoTracking);
 };
 
 
 }  // namespace tracked_objects
 
 #endif  // BASE_TRACKED_OBJECTS_H_