[ash/shelf] ResourceBundle should be used as pointer not non-const ref

ash/shelf/overflow_button.cc

Index: ash/shelf/overflow_button.cc
diff --git a/ash/shelf/overflow_button.cc b/ash/shelf/overflow_button.cc
index 5e6c607723d771e89fd5f6d2200006cd657ed324..79b2bcdfa040953c4276430ba38325b0978660a6 100644
--- a/ash/shelf/overflow_button.cc
+++ b/ash/shelf/overflow_button.cc
@@ -37,9 +37,8 @@ const int kBackgroundOffset = (48 - kButtonHoverSize) / 2;
 OverflowButton::OverflowButton(views::ButtonListener* listener)
     : CustomButton(listener),
       bottom_image_(NULL) {
-  ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
-  bottom_image_ = rb.GetImageNamed(IDR_ASH_SHELF_OVERFLOW).ToImageSkia();
-
+  ui::ResourceBundle* rb = &ui::ResourceBundle::GetSharedInstance();
+  bottom_image_ = rb->GetImageNamed(IDR_ASH_SHELF_OVERFLOW).ToImageSkia();
 
   SetAccessibilityFocusable(true);
   SetAccessibleName(l10n_util::GetStringUTF16(IDS_ASH_SHELF_OVERFLOW_NAME));