Detailed heap snapshot usability improvement.

Detailed heap snapshot usability improvement.

The detailed heap snapshot has two groups of nodes. The first one
is the group for v8 heap nodes and the second one is the group for
native objects. At the moment we have two different sets of native
objects. There are 'Detached DOM trees' and 'Document DOM trees' type of objects.

I think it'd be nice to replace one group containing all native objects with
separate groups for different types of native objects.

BUG=none
TEST=HeapSnapshotRetainedObjectInfo

Review URL: https://chromiumcodereview.appspot.com/9223009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10528 ce2b1a6d-e550-0410-aec6-3dcde31c8c00