assistant: allow assistant consent status pref in autotest api

BUG=b:162421778

Change-Id: I3e93cabe5791930f8ce793e569af0152193749d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2367512Reviewed-by: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Jeffrey Young <cowmoo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801150}

chrome/browser/chromeos/extensions/autotest_private/autotest_private_api.cc

@@ -426,6 +426,12 @@ std::string SetWhitelistedPref(Profile* profile,
       return base::StringPrintf("Assistant not allowed - state: %d",
                                 allowed_state);
     }
+  } else if (pref_name == chromeos::assistant::prefs::kAssistantConsentStatus) {
+    DCHECK(value.is_int());
+    if (!profile->GetPrefs()->GetBoolean(
+            chromeos::assistant::prefs::kAssistantEnabled)) {
+      return "Unable to set the pref because Assistant has not been enabled.";
+    }
   } else if (pref_name ==
                  chromeos::assistant::prefs::kAssistantContextEnabled ||
              pref_name ==