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 <zeuthen@chromium.org>
Reviewed-by: David Zeuthen <zeuthen@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
diff --git a/mock_payload_state.h b/mock_payload_state.h
index c32ff78..fe744de 100644
--- a/mock_payload_state.h
+++ b/mock_payload_state.h
@@ -31,6 +31,7 @@
   MOCK_METHOD0(GetPayloadAttemptNumber, uint32_t());
   MOCK_METHOD0(GetUrlIndex, uint32_t());
   MOCK_METHOD0(GetUrlFailureCount, uint32_t());
+  MOCK_METHOD0(GetUrlSwitchCount, uint32_t());
   MOCK_METHOD0(GetBackoffExpiryTime, base::Time());
   MOCK_METHOD0(GetUpdateDuration, base::TimeDelta());
   MOCK_METHOD0(GetUpdateDurationUptime, base::TimeDelta());