Tweak compaction candidate selection to avoid keeping page with low occupancy around.

Tweak compaction candidate selection to avoid keeping page with low occupancy around.

Increase slots buffer chain length to 15 to make compaction more aggressive and usefull.

Pass gc and collector selection reasons to GCTracer to allow more meaningull --gc-trace.

Print fragmentation of spaces that we do not compact.

R=erik.corry@gmail.com

Review URL: https://chromiumcodereview.appspot.com/9323007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10601 ce2b1a6d-e550-0410-aec6-3dcde31c8c00