Fix Mac browser crash in BookmarkMenuBridge::UpdateMenu.

chrome/browser/cocoa/bookmark_menu_bridge.mm

Index: chrome/browser/cocoa/bookmark_menu_bridge.mm
diff --git a/chrome/browser/cocoa/bookmark_menu_bridge.mm b/chrome/browser/cocoa/bookmark_menu_bridge.mm
index d9742248d3757e8bf655b0be4b22b98fb0852a8b..006b10b1311093291bd27eb83d407eb975c59e51 100644
--- a/chrome/browser/cocoa/bookmark_menu_bridge.mm
+++ b/chrome/browser/cocoa/bookmark_menu_bridge.mm
@@ -47,6 +47,9 @@ void BookmarkMenuBridge::UpdateMenu(NSMenu* bookmark_menu) {
   DCHECK(bookmark_menu);
   if (menuIsValid_)
     return;
+  BookmarkModel* model = GetBookmarkModel();
+  if (!model || !model->IsLoaded())
+    return;
 
   if (!folder_image_) {
     ResourceBundle& rb = ResourceBundle::GetSharedInstance();
@@ -56,7 +59,8 @@ void BookmarkMenuBridge::UpdateMenu(NSMenu* bookmark_menu) {
   ClearBookmarkMenu(bookmark_menu);
 
   // Add bookmark bar items, if any.
-  const BookmarkNode* barNode = GetBookmarkModel()->GetBookmarkBarNode();
+  const BookmarkNode* barNode = model->GetBookmarkBarNode();
+  CHECK(barNode);
   if (barNode->GetChildCount()) {
     [bookmark_menu addItem:[NSMenuItem separatorItem]];
     AddNodeToMenu(barNode, bookmark_menu);
@@ -67,7 +71,7 @@ void BookmarkMenuBridge::UpdateMenu(NSMenu* bookmark_menu) {
     l10n_util::GetString(IDS_BOOMARK_BAR_OTHER_FOLDER_NAME));
   [bookmark_menu addItem:[NSMenuItem separatorItem]];
   AddNodeAsSubmenu(bookmark_menu,
-                   GetBookmarkModel()->other_node(),
+                   model->other_node(),
                    other_items_title);
 
   menuIsValid_ = true;