update_engine: Report VPD write failure to UMA

Currently we see many first actives to come from non-FSI images. But we have not
been able to figure out why. This CL, reports a new error
kFirstActiveOmahaPingSentPersistenceError when writing the first active omaha
flag into VPD fails. This allows us to see if that is the actual cause of the
problem.

CL:1062659 adds the enum value on the Chrome side.

BUG=chromium:833980
TEST=unittests
TEST=precq

Change-Id: I65e233c5f895489ba905494fb20d7b00d0c4af10
Reviewed-on: https://chromium-review.googlesource.com/1062662
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
diff --git a/metrics_reporter_omaha.h b/metrics_reporter_omaha.h
index c19fe86..344cff8 100644
--- a/metrics_reporter_omaha.h
+++ b/metrics_reporter_omaha.h
@@ -143,6 +143,8 @@
 
   void ReportInstallDateProvisioningSource(int source, int max) override;
 
+  void ReportInternalErrorCode(ErrorCode error_code) override;
+
  private:
   friend class MetricsReporterOmahaTest;