This will give us the ability to keep entries_ list sorted by id.
And based on that fact we will be able to use it for:
1) GetNodeById method and drop sorted version of entries list in HeapSnapshot;
2) building heap stats;
3) doing the fill stage instead of second iteration over heap.

BUG=none
TEST=none
R=yurys

Review URL: https://chromiumcodereview.appspot.com/10031032

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11259 ce2b1a6d-e550-0410-aec6-3dcde31c8c00