Improve documentation of potential memory leaks in URLMatcherFactory

chrome/common/extensions/matcher/url_matcher.h

 // 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.
 
 #ifndef CHROME_COMMON_EXTENSIONS_MATCHER_URL_MATCHER_H_
 #define CHROME_COMMON_EXTENSIONS_MATCHER_URL_MATCHER_H_
 #pragma once
 
 #include <set>
 #include <vector>
@@ skipping 95 matching lines @@
 // all created URLMatcherCondition and the SubstringSetMatcher.
 class URLMatcherConditionFactory {
  public:
   URLMatcherConditionFactory();
   ~URLMatcherConditionFactory();
 
   // Canonicalizes a URL for "Create{Host,Path,Query}*Condition" searches.
   std::string CanonicalizeURLForComponentSearches(const GURL& url);
 
   // Factory methods for various condition types.
+  //
+  // Note that these methods fill the pattern_singletons_. If you create
+  // conditions and don't register them to a URLMatcher, they will continue to
+  // consume memory. You need to call ForgetUnusedPatterns() or
+  // URLMatcher::ClearUnusedConditionSets() in this case.
   URLMatcherCondition CreateHostPrefixCondition(const std::string& prefix);
   URLMatcherCondition CreateHostSuffixCondition(const std::string& suffix);
   URLMatcherCondition CreateHostContainsCondition(const std::string& str);
   URLMatcherCondition CreateHostEqualsCondition(const std::string& str);
 
   URLMatcherCondition CreatePathPrefixCondition(const std::string& prefix);
   URLMatcherCondition CreatePathSuffixCondition(const std::string& suffix);
   URLMatcherCondition CreatePathContainsCondition(const std::string& str);
   URLMatcherCondition CreatePathEqualsCondition(const std::string& str);
 
@@ skipping 184 matching lines @@
   SubstringSetMatcher url_component_matcher_;
   std::set<const SubstringPattern*> registered_full_url_patterns_;
   std::set<const SubstringPattern*> registered_url_component_patterns_;
 
   DISALLOW_COPY_AND_ASSIGN(URLMatcher);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_MATCHER_URL_MATCHER_H_