Bring up of the enhanced bookmarks cluster service.

components/enhanced_bookmarks/enhanced_bookmark_model.cc

Index: components/enhanced_bookmarks/enhanced_bookmark_model.cc
diff --git a/components/enhanced_bookmarks/enhanced_bookmark_model.cc b/components/enhanced_bookmarks/enhanced_bookmark_model.cc
index 6ffcaf392035cd2101e9fbbf356985a9464c6630..7f89f8297eb6ca451377207e7e39fe0958063fb3 100644
--- a/components/enhanced_bookmarks/enhanced_bookmark_model.cc
+++ b/components/enhanced_bookmarks/enhanced_bookmark_model.cc
@@ -91,15 +91,18 @@ EnhancedBookmarkModel::EnhancedBookmarkModel(BookmarkModel* bookmark_model,
 }
 
 EnhancedBookmarkModel::~EnhancedBookmarkModel() {
+  Shutdown();
 }
 
 void EnhancedBookmarkModel::Shutdown() {
-  FOR_EACH_OBSERVER(EnhancedBookmarkModelObserver,
-                    observers_,
-                    EnhancedBookmarkModelShuttingDown());
-  weak_ptr_factory_.InvalidateWeakPtrs();
-  bookmark_model_->RemoveObserver(this);
-  bookmark_model_ = NULL;
+  if (bookmark_model_) {
+    FOR_EACH_OBSERVER(EnhancedBookmarkModelObserver,
+                      observers_,
+                      EnhancedBookmarkModelShuttingDown());
+    weak_ptr_factory_.InvalidateWeakPtrs();
+    bookmark_model_->RemoveObserver(this);
+    bookmark_model_ = NULL;
+  }
 }
 
 void EnhancedBookmarkModel::AddObserver(