Add UMA for signin through NTP content suggestions.

components/signin/core/browser/signin_metrics.h

Index: components/signin/core/browser/signin_metrics.h
diff --git a/components/signin/core/browser/signin_metrics.h b/components/signin/core/browser/signin_metrics.h
index a83851cf7f1c6a7b897c4b559fca975b41cee6c3..4d227e62690f405a2bfb560c3f5442062c918e09 100644
--- a/components/signin/core/browser/signin_metrics.h
+++ b/components/signin/core/browser/signin_metrics.h
@@ -139,6 +139,7 @@ enum class AccessPoint : int {
   ACCESS_POINT_UNKNOWN,  // This should never have been used to get signin URL.
   ACCESS_POINT_PASSWORD_BUBBLE,
   ACCESS_POINT_AUTOFILL_DROPDOWN,
+  ACCESS_POINT_NTP_CONTENT_SUGGESTIONS,
   ACCESS_POINT_MAX,  // This must be last.
 };