The serialized node structure currently holds an index
of its first containment edge in the edges array.
The index can be quite big (up to 7 digits for large snapshots).
The patch changes the serialization format to pass
node containment edge count instead. For most nodes the count
is just a single digit number.
This reduces serialized snapshot size and therefore its transfer time.

Review URL: https://chromiumcodereview.appspot.com/10534008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11728 ce2b1a6d-e550-0410-aec6-3dcde31c8c00