Added CHECKs for null pointers in ChromeAppSorting.

extensions/browser/extension_prefs.cc

Index: extensions/browser/extension_prefs.cc
diff --git a/extensions/browser/extension_prefs.cc b/extensions/browser/extension_prefs.cc
index c4f7da2e79013c6ba7d1be3ff6de6c4d5903cb70..ecf9e88848108e40287e953d6acf1357c287d494 100644
--- a/extensions/browser/extension_prefs.cc
+++ b/extensions/browser/extension_prefs.cc
@@ -1867,6 +1867,9 @@ ExtensionPrefs::ExtensionPrefs(
       time_provider_(time_provider.Pass()),
       extensions_disabled_(extensions_disabled) {
   app_sorting_->SetExtensionScopedPrefs(this);
+  // TODO(mgiuca): Added this CHECK to try and diagnose http://crbug.com/476648.
+  // Remove it after the investigation is concluded.
+  app_sorting_->CheckExtensionScopedPrefs();
   MakePathsRelative();
 
   // Ensure that any early observers are watching before prefs are initialized.