Ignore invalid managed user settings values gracefully.

chrome/browser/supervised_user/supervised_user_settings_service.cc

Index: chrome/browser/supervised_user/supervised_user_settings_service.cc
diff --git a/chrome/browser/supervised_user/supervised_user_settings_service.cc b/chrome/browser/supervised_user/supervised_user_settings_service.cc
index 6628c217b971eae0cc53a31dfcc1dc00efbd5a72..33e9f25b7a36f29376fa20d6408f1d15dc1e4b01 100644
--- a/chrome/browser/supervised_user/supervised_user_settings_service.cc
+++ b/chrome/browser/supervised_user/supervised_user_settings_service.cc
@@ -241,6 +241,14 @@ SyncMergeResult SupervisedUserSettingsService::MergeDataAndStartSyncing(
         sync_data.GetSpecifics().managed_user_setting();
     std::unique_ptr<base::Value> value =
         JSONReader::Read(supervised_user_setting.value());
+    // null values will cause Chrome to crash when building the settings
+    // dictionary.  Therefore, we ignore them here to prevent such crashes.

[Marc Treib, 2016/08/03 15:30:16]

Just say that SetWithoutPathExpansion below requires non-null values.
Also maybe mention *why* null values can occur here: For wrongly formatted
input.
Finally, nit: Start comment with a capital letter.

+    if (!value) {
+      DLOG(ERROR) << "Invalid managed user setting value: "
+                  << supervised_user_setting.value()
+                  << ". Values must be JSON values.";
+      continue;
+    }
     std::string name_suffix = supervised_user_setting.name();
     std::string name_key = name_suffix;
     base::DictionaryValue* dict = GetDictionaryAndSplitKey(&name_suffix);