Refactoring: Move prefs constants out to the constants.h/cc

Adding/removing the set of keys used by various parts of the Update Engine code
does not affect the implementation of the prefs module, hence separating them.

BUG=chromium:229090
TEST=Unit tests pass.

Change-Id: Id774b726a47b461e563e2e413527054e4da0c012
Reviewed-on: https://gerrit.chromium.org/gerrit/47593
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Tested-by: Jay Srinivasan <jaysri@chromium.org>
Commit-Queue: Jay Srinivasan <jaysri@chromium.org>
diff --git a/constants.h b/constants.h
index d6fd736..5bba2d3 100644
--- a/constants.h
+++ b/constants.h
@@ -14,6 +14,31 @@
 // The contents of the powerwash marker file.
 extern const char kPowerwashCommand[];
 
+// Constants related to preferences.
+extern const char kPrefsBackoffExpiryTime[];
+extern const char kPrefsCertificateReportToSendDownload[];
+extern const char kPrefsCertificateReportToSendUpdate[];
+extern const char kPrefsCurrentResponseSignature[];
+extern const char kPrefsCurrentUrlFailureCount[];
+extern const char kPrefsCurrentUrlIndex[];
+extern const char kPrefsDeltaUpdateFailures[];
+extern const char kPrefsLastActivePingDay[];
+extern const char kPrefsLastRollCallPingDay[];
+extern const char kPrefsManifestMetadataSize[];
+extern const char kPrefsPayloadAttemptNumber[];
+extern const char kPrefsPreviousVersion[];
+extern const char kPrefsResumedUpdateFailures[];
+extern const char kPrefsUpdateCheckCount[];
+extern const char kPrefsUpdateCheckResponseHash[];
+extern const char kPrefsUpdateFirstSeenAt[];
+extern const char kPrefsUpdateServerCertificate[];
+extern const char kPrefsUpdateStateNextDataOffset[];
+extern const char kPrefsUpdateStateNextOperation[];
+extern const char kPrefsUpdateStateSHA256Context[];
+extern const char kPrefsUpdateStateSignatureBlob[];
+extern const char kPrefsUpdateStateSignedSHA256Context[];
+extern const char kPrefsWallClockWaitPeriod[];
+
 }  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_CONSTANTS_H