Introduce a new framework for back-and-forth tracked/protected preferences migration.

chrome/browser/prefs/chrome_pref_service_factory.cc

Index: chrome/browser/prefs/chrome_pref_service_factory.cc
diff --git a/chrome/browser/prefs/chrome_pref_service_factory.cc b/chrome/browser/prefs/chrome_pref_service_factory.cc
index 0f1d01be1e5e053e78ec0f8b460a1c1f1af6fe62..5546942d14b602f35060ff79ba30cc0f55bdd549 100644
--- a/chrome/browser/prefs/chrome_pref_service_factory.cc
+++ b/chrome/browser/prefs/chrome_pref_service_factory.cc
@@ -158,10 +158,25 @@ const PrefHashFilter::TrackedPreferenceMetadata kTrackedPrefs[] = {
     PrefHashFilter::NO_ENFORCEMENT,
     PrefHashFilter::TRACKING_STRATEGY_ATOMIC
   },
+  {
+    // Protecting kPreferenceResetTime does two things:
+    //  1) It ensures this isn't accidently set by someone stomping the pref
+    //     file.
+    //  2) More importantly, it declares kPreferenceResetTime as a protected
+    //     pref which is required for it to be visible when queried via the
+    //     SegregatedPrefStore. This is because it's written directly in the
+    //     protected JsonPrefStore by that store's PrefHashFilter if there was
+    //     a reset in FilterOnLoad and SegregatedPrefStore will not look for it
+    //     in the protected JsonPrefStore unless it's declared as a protected
+    //     preference here.
+    15, prefs::kPreferenceResetTime,
+    PrefHashFilter::ENFORCE_ON_LOAD,
+    PrefHashFilter::TRACKING_STRATEGY_ATOMIC
+  },
 };
 
 // The count of tracked preferences IDs across all platforms.
-const size_t kTrackedPrefsReportingIDsCount = 15;
+const size_t kTrackedPrefsReportingIDsCount = 16;
 COMPILE_ASSERT(kTrackedPrefsReportingIDsCount >= arraysize(kTrackedPrefs),
                need_to_increment_ids_count);