Make LinkedStack.h use FastAlloc

This is a speculative fix for
https://code.google.com/p/chromium/issues/detail?id=253132. We need to be able
to create the nodes in the linked list efficiently, which means that we don't
want to use the system allocator on Mac because it is slow.

BUG=253132
R=tonyg

Review URL: https://chromiumcodereview.appspot.com/17551015

git-svn-id: svn://svn.chromium.org/blink/trunk@152934 bbb929c8-8fbe-4397-9dbb-9b2b20218538