Enable parallel sweeping.

BUG=

Review URL: https://codereview.chromium.org/12255002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13650 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -430,7 +430,7 @@ DEFINE_bool(trace_incremental_marking, false,
             "trace progress of the incremental marking")
 DEFINE_bool(track_gc_object_stats, false,
             "track object counts and memory usage")
-DEFINE_bool(parallel_sweeping, false, "enable parallel sweeping")
+DEFINE_bool(parallel_sweeping, true, "enable parallel sweeping")
 DEFINE_bool(concurrent_sweeping, false, "enable concurrent sweeping")
 DEFINE_int(sweeper_threads, 1,
            "number of parallel and concurrent sweeping threads")