Invoke the StartSyncFlare for prefs when performing an automatic reset.

chrome/browser/prefs/profile_pref_store_manager.cc

Index: chrome/browser/prefs/profile_pref_store_manager.cc
diff --git a/chrome/browser/prefs/profile_pref_store_manager.cc b/chrome/browser/prefs/profile_pref_store_manager.cc
index f4264b78014f8d34676a41f65ded519f92d0aa01..edee0251e37f59799cc624f2d7e955928a8b074d 100644
--- a/chrome/browser/prefs/profile_pref_store_manager.cc
+++ b/chrome/browser/prefs/profile_pref_store_manager.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/prefs/profile_pref_store_manager.h"
 
 #include "base/bind.h"
+#include "base/callback.h"
 #include "base/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/logging.h"
@@ -16,9 +17,11 @@
 #include "chrome/browser/prefs/tracked/pref_service_hash_store_contents.h"
 #include "chrome/browser/prefs/tracked/segregated_pref_store.h"
 #include "chrome/browser/prefs/tracked/tracked_preferences_migration.h"
+#include "chrome/browser/sync/glue/sync_start_util.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/pref_names.h"
 #include "components/pref_registry/pref_registry_syncable.h"
+#include "sync/internal_api/public/base/model_type.h"
 
 // TODO(erikwright): Enable this on Chrome OS and Android once MACs are moved
 // out of Local State. This will resolve a race condition on Android and a
@@ -108,15 +111,27 @@ PersistentPrefStore* ProfilePrefStoreManager::CreateProfilePrefStore(
     }
   }
 
+  // Used to kick sync early in case of a reset event. This is done since sync
+  // may bring back the user's server value post-reset which could potentially
+  // cause a "settings flash" between the factory default and the
+  // re-instantiated server value. Starting sync ASAP minimizes the window
+  // before the server value is re-instantiated (this window can otherwise be
+  // as long as 10 seconds by default).
+  const base::Closure start_sync_flare_for_prefs =

[erikwright (departed), 2014/07/16 20:23:43]

This should be a dependency passed in by chrome_pref_service_factory, not a
static access in this class. That will be much more testable.

[gab, 2014/07/16 20:30:39]

How is it more testable? I thought about it, but I'm not sure that another layer
of piping gives us anything here... The |on_reset| callback is already tested in
pref_hash_filter_unittest.cc; testing that the flare itself is called would
likely require a huge test (involving services et al.) and I'm not convinced
that's truly required for such a simple hook.

+      base::Bind(sync_start_util::GetFlareForSyncableService(profile_path_),
+                 syncer::PREFERENCES);
+
   scoped_ptr<PrefHashFilter> unprotected_pref_hash_filter(
       new PrefHashFilter(GetPrefHashStore(false),
                          unprotected_configuration,
+                         base::Closure(),
                          validation_delegate,
                          reporting_ids_count_,
                          false));
   scoped_ptr<PrefHashFilter> protected_pref_hash_filter(
       new PrefHashFilter(GetPrefHashStore(true),
                          protected_configuration,
+                         start_sync_flare_for_prefs,
                          validation_delegate,
                          reporting_ids_count_,
                          true));
@@ -175,6 +190,7 @@ bool ProfilePrefStoreManager::InitializePrefsFromMasterPrefs(
     to_serialize = copy.get();
     PrefHashFilter(GetPrefHashStore(false),
                    tracking_configuration_,
+                   base::Closure(),
                    NULL,
                    reporting_ids_count_,
                    false).Initialize(copy.get());
@@ -209,6 +225,7 @@ ProfilePrefStoreManager::CreateDeprecatedCombinedProfilePrefStore(
     pref_filter.reset(
         new PrefHashFilter(pref_hash_store_impl.PassAs<PrefHashStore>(),
                            tracking_configuration_,
+                           base::Closure(),
                            NULL,
                            reporting_ids_count_,
                            false));