Add metric to report number of URL switches per update attempt

BUG=chromium:226765
TEST=Existing unit tests modified to test feature, Unit tests pass

Change-Id: I5ee0816cac3fa4fa641949ed4872aef8074e3fcc
Reviewed-on: https://gerrit.chromium.org/gerrit/48537
Commit-Queue: David Zeuthen <[email protected]>
Reviewed-by: David Zeuthen <[email protected]>
Tested-by: David Zeuthen <[email protected]>
diff --git a/constants.cc b/constants.cc
index 3064c40..0bc95f7 100644
--- a/constants.cc
+++ b/constants.cc
@@ -31,6 +31,7 @@
 const char kPrefsTotalBytesDownloaded[] = "total-bytes-downloaded";
 const char kPrefsUpdateCheckCount[] = "update-check-count";
 const char kPrefsUpdateCheckResponseHash[] = "update-check-response-hash";
+const char kPrefsUpdateDurationUptime[] = "update-duration-uptime";
 const char kPrefsUpdateFirstSeenAt[] = "update-first-seen-at";
 const char kPrefsUpdateServerCertificate[] = "update-server-cert";
 const char kPrefsUpdateStateNextDataOffset[] = "update-state-next-data-offset";
@@ -39,8 +40,8 @@
 const char kPrefsUpdateStateSignatureBlob[] = "update-state-signature-blob";
 const char kPrefsUpdateStateSignedSHA256Context[] =
     "update-state-signed-sha-256-context";
-const char kPrefsWallClockWaitPeriod[] = "wall-clock-wait-period";
 const char kPrefsUpdateTimestampStart[] = "update-timestamp-start";
-const char kPrefsUpdateDurationUptime[] = "update-duration-uptime";
+const char kPrefsUrlSwitchCount[] = "url-switch-count";
+const char kPrefsWallClockWaitPeriod[] = "wall-clock-wait-period";
 
 }