Enable native parent access code validation for online login.

Since there is no server side dependencies, we decided to enable the
feature by default. The feature flag will be used as killer-switch
in case anything goes wrong and clean up in future milestones.

Bug: 921142
Test: manual tests
Change-Id: Ibc849d549a394b6487626e6d71435a14e76e9ad6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2348010
Commit-Queue: Li Lin <llin@chromium.org>
Reviewed-by: Aga Wronska <agawronska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796908}

chrome/common/chrome_features.cc

@@ -575,7 +575,7 @@ const base::Feature kParentAccessCode{"ParentAccessCode",
 // Enables usage of Parent Access Code in the login flow for reauth and add
 // user. Requires |kParentAccessCode| to be enabled.
 const base::Feature kParentAccessCodeForOnlineLogin{
-    "ParentAccessCodeForOnlineLogin", base::FEATURE_DISABLED_BY_DEFAULT};
+    "ParentAccessCodeForOnlineLogin", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enables usage of Parent Access Code to authorize change of time actions on
 // child user device. Requires |kParentAccessCode| to be enabled.