[sync] DualLayerUserPrefStore: Use json prefstore for account by default

Enables feature to switch to use json/persistent pref store for account
preferences by default.

(cherry picked from commit 4d4b30b)

Bug: 1447588
Change-Id: I6787c6c9f76c5631220effa198398ef70d07fe2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4568221
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Ankush Singh <ankushkush@google.com>
Cr-Original-Commit-Position: refs/heads/main@{#1151125}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4574368
Cr-Commit-Position: refs/branch-heads/5790@{#262}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

components/sync/base/features.cc

@@ -167,6 +167,6 @@ BASE_FEATURE(kSyncIgnoreGetUpdatesRetryDelay,
 
 BASE_FEATURE(kSyncEnablePersistentStorageForAccountPreferences,
              "SyncEnablePersistentStorageForAccountPreferences",
-             base::FEATURE_DISABLED_BY_DEFAULT);
+             base::FEATURE_ENABLED_BY_DEFAULT);
 
 }  // namespace syncer