Ensure that --disable-extensions disables extension prefs from being enacted

chrome/browser/extensions/test_extension_prefs.h

Index: chrome/browser/extensions/test_extension_prefs.h
diff --git a/chrome/browser/extensions/test_extension_prefs.h b/chrome/browser/extensions/test_extension_prefs.h
index 1723e560171766d9c51d31cdce48e7dcdb944d7b..25862dd42669da0b238c11fd780f436aa4ac4521 100644
--- a/chrome/browser/extensions/test_extension_prefs.h
+++ b/chrome/browser/extensions/test_extension_prefs.h
@@ -61,6 +61,10 @@ class TestExtensionPrefs {
 
   PrefService* CreateIncognitoPrefService() const;
 
+  // Allows disabling the loading of preferences of extensions. Becomes
+  // active after calling RecreateExtensionPrefs(). Defaults to false.
+  void set_extensions_disabled(bool extensions_disabled);
+
  protected:
   ScopedTempDir temp_dir_;
   FilePath preferences_file_;
@@ -70,6 +74,7 @@ class TestExtensionPrefs {
   scoped_ptr<ExtensionPrefValueMap> extension_pref_value_map_;
 
  private:
+  bool extensions_disabled_;
   DISALLOW_COPY_AND_ASSIGN(TestExtensionPrefs);
 };