Mac: Use native folder icons for the bookmark bar.

chrome/browser/cocoa/bookmark_bar_controller.mm

Index: chrome/browser/cocoa/bookmark_bar_controller.mm
diff --git a/chrome/browser/cocoa/bookmark_bar_controller.mm b/chrome/browser/cocoa/bookmark_bar_controller.mm
index 142d669cd5f51588045a9be8c023021ef8afe843..1e01ab5f9cd9dd2d6f61233e1e53bbf6f2c4f70a 100644
--- a/chrome/browser/cocoa/bookmark_bar_controller.mm
+++ b/chrome/browser/cocoa/bookmark_bar_controller.mm
@@ -68,7 +68,8 @@
 
   for (NSObject* item in itemsPendingBookmarkIcon_.get()) {
     DCHECK([item respondsToSelector:@selector(setImage:)]);
-    if ([item respondsToSelector:@selector(setImage:)]) {
+    if ([item retainCount] > 1 &&
+        [item respondsToSelector:@selector(setImage:)]) {
       // |item| is not really of type |NSCell*|, but some type that responds to
       // |setImage:| is required to shut up a compiler warning.
       [(NSCell*)item setImage:folderImage_];