Adding a SQL implementation of the backing store for previews opt outs

chrome/common/chrome_constants.h

Index: chrome/common/chrome_constants.h
diff --git a/chrome/common/chrome_constants.h b/chrome/common/chrome_constants.h
index aa19c4b5f38e2a1937f3ec3861e56ee1d67067d3..1083f8dad69634dd6de10efa1854c451697c0f3b 100644
--- a/chrome/common/chrome_constants.h
+++ b/chrome/common/chrome_constants.h
@@ -52,20 +52,21 @@ extern const base::FilePath::CharType kExtensionsCookieFilename[];
 extern const base::FilePath::CharType kFirstRunSentinel[];
 extern const base::FilePath::CharType kGCMStoreDirname[];
 extern const base::FilePath::CharType kLocalStateFilename[];
 extern const base::FilePath::CharType kLocalStorePoolName[];
 extern const base::FilePath::CharType kMediaCacheDirname[];
 extern const base::FilePath::CharType kNetworkPersistentStateFilename[];
 extern const base::FilePath::CharType kOfflinePageArchivesDirname[];
 extern const base::FilePath::CharType kOfflinePageMetadataDirname[];
 extern const base::FilePath::CharType kOfflinePageRequestQueueDirname[];
 extern const base::FilePath::CharType kPreferencesFilename[];
+extern const base::FilePath::CharType kPreviewsOptOutDirname[];
 extern const base::FilePath::CharType kProtectedPreferencesFilenameDeprecated[];
 extern const base::FilePath::CharType kReadmeFilename[];
 extern const base::FilePath::CharType kSafeBrowsingBaseFilename[];
 extern const base::FilePath::CharType kSecurePreferencesFilename[];
 extern const base::FilePath::CharType kServiceStateFileName[];
 extern const base::FilePath::CharType kSingletonCookieFilename[];
 extern const base::FilePath::CharType kSingletonLockFilename[];
 extern const base::FilePath::CharType kSingletonSocketFilename[];
 extern const base::FilePath::CharType kSupervisedUserSettingsFilename[];
 extern const base::FilePath::CharType kThemePackFilename[];