Make Sber1/2 pref metrics into Nullable Booleans so we can track how often these prefs are unset.

components/safe_browsing_db/safe_browsing_prefs_unittest.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <string>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/strings/string_util.h"
 #include "base/test/scoped_feature_list.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/testing_pref_service.h"
 #include "components/safe_browsing_db/safe_browsing_prefs.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace safe_browsing {
 
 class SafeBrowsingPrefsTest : public ::testing::Test {
  protected:
   void SetUp() override {
     prefs_.registry()->RegisterBooleanPref(
         prefs::kSafeBrowsingExtendedReportingEnabled, false);
     prefs_.registry()->RegisterBooleanPref(
         prefs::kSafeBrowsingScoutReportingEnabled, false);
     prefs_.registry()->RegisterBooleanPref(
         prefs::kSafeBrowsingScoutGroupSelected, false);
+    prefs_.registry()->RegisterBooleanPref(
+        prefs::kSafeBrowsingSawInterstitialExtendedReporting, false);
+    prefs_.registry()->RegisterBooleanPref(
+        prefs::kSafeBrowsingSawInterstitialScoutReporting, false);
 
     ResetExperiments(/*can_show_scout=*/false, /*only_show_scout=*/false);
   }
 
   void ResetPrefs(bool sber_reporting, bool scout_reporting, bool scout_group) {
     prefs_.SetBoolean(prefs::kSafeBrowsingExtendedReportingEnabled,
                       sber_reporting);
     prefs_.SetBoolean(prefs::kSafeBrowsingScoutReportingEnabled,
                       scout_reporting);
     prefs_.SetBoolean(prefs::kSafeBrowsingScoutGroupSelected, scout_group);
@@ skipping 411 matching lines @@
   EXPECT_EQ(SBER_LEVEL_OFF, GetExtendedReportingLevel(prefs_));
   // Turning on Scout gives us Scout level reporting
   ResetPrefs(/*sber=*/false, /*scout_reporting=*/true, /*scout_group=*/true);
   EXPECT_EQ(SBER_LEVEL_SCOUT, GetExtendedReportingLevel(prefs_));
   // .. and the legacy pref doesn't affect this.
   ResetPrefs(/*sber=*/true, /*scout_reporting=*/true, /*scout_group=*/true);
   EXPECT_EQ(SBER_LEVEL_SCOUT, GetExtendedReportingLevel(prefs_));
 }
 
 }  // namespace safe_browsing