Reduce the memory usage of bookmarks storage

components/bookmarks/browser/bookmark_node.h

Index: components/bookmarks/browser/bookmark_node.h
diff --git a/components/bookmarks/browser/bookmark_node.h b/components/bookmarks/browser/bookmark_node.h
index d125c44e52c92806cea31a7297925411baba0182..1c91d393fded2ed3cd84c1aa56cf8c539e5559bb 100644
--- a/components/bookmarks/browser/bookmark_node.h
+++ b/components/bookmarks/browser/bookmark_node.h
@@ -69,7 +69,7 @@ class BookmarkNode : public ui::TreeNode<BookmarkNode>, public TitledUrlNode {
 
   // Returns the favicon's URL. Returns an empty URL if there is no favicon
   // associated with this bookmark.
-  const GURL& icon_url() const { return icon_url_; }
+  const GURL* icon_url() const { return icon_url_ ? icon_url_.get() : nullptr; }
 
   Type type() const { return type_; }
   void set_type(Type type) { type_ = type; }
@@ -134,7 +134,7 @@ class BookmarkNode : public ui::TreeNode<BookmarkNode>, public TitledUrlNode {
 
   // Sets the favicon's URL.
   void set_icon_url(const GURL& icon_url) {
-    icon_url_ = icon_url;
+    icon_url_.reset(new GURL(icon_url));
   }
 
   // Returns the favicon. In nearly all cases you should use the method
@@ -179,7 +179,7 @@ class BookmarkNode : public ui::TreeNode<BookmarkNode>, public TitledUrlNode {
   favicon_base::IconType favicon_type_;
 
   // The URL of the node's favicon.
-  GURL icon_url_;
+  std::unique_ptr<GURL> icon_url_;
 
   // The loading state of the favicon.
   FaviconState favicon_state_;