Remove unused variable declaration.

This issue was found by a linter.

R=battre@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/22844003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@217619 0039d316-1c4b-4281-b951-d872f2087c98

extensions/common/matcher/regex_set_matcher.cc

@@ -53,7 +53,6 @@ bool RegexSetMatcher::Match(const std::string& text,
   std::vector<RE2ID> re2_ids;
   filtered_re2_->AllMatches(text, atoms, &re2_ids);
 
-  std::set<StringPattern::ID> matched_ids;
   for (size_t i = 0; i < re2_ids.size(); ++i) {
     StringPattern::ID id = re2_id_map_[re2_ids[i]];
     matches->insert(id);