Improve documentation of potential memory leaks in URLMatcherFactory

chrome/common/extensions/matcher/url_matcher.h

Index: chrome/common/extensions/matcher/url_matcher.h
diff --git a/chrome/common/extensions/matcher/url_matcher.h b/chrome/common/extensions/matcher/url_matcher.h
index 4945e8a2d7c23696dd744c05448ae25d41836944..eef01d52a4ceb7a0ad51d986cbe98022dafcc8be 100644
--- a/chrome/common/extensions/matcher/url_matcher.h
+++ b/chrome/common/extensions/matcher/url_matcher.h
@@ -113,6 +113,11 @@ class URLMatcherConditionFactory {
   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);