bookmarks: Fix mistakes found by cppcheck.

chrome/browser/bookmarks/bookmark_index_unittest.cc

Index: chrome/browser/bookmarks/bookmark_index_unittest.cc
diff --git a/chrome/browser/bookmarks/bookmark_index_unittest.cc b/chrome/browser/bookmarks/bookmark_index_unittest.cc
index d92cdb99dbf16569030099938e93ea7adae367cf..d2ab50386c6dcc153f18776deb06ec9bd9c41842 100644
--- a/chrome/browser/bookmarks/bookmark_index_unittest.cc
+++ b/chrome/browser/bookmarks/bookmark_index_unittest.cc
@@ -51,7 +51,7 @@ class BookmarkIndexTest : public testing::Test {
   }
 
   void ExpectMatches(const std::string& query,
-                     const std::vector<std::string> expected_titles) {
+                     const std::vector<std::string>& expected_titles) {
     std::vector<bookmark_utils::TitleMatch> matches;
     model_->GetBookmarksWithTitlesMatching(ASCIIToUTF16(query), 1000, &matches);
     ASSERT_EQ(expected_titles.size(), matches.size());