Implement progress bar for large objects.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 694dbea562ef8511403d8fc7c1df099c3e763e67..0863f7de95a03037f73447d61d17b2bb3feb35e4 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -438,6 +438,9 @@ DEFINE_bool(incremental_code_compaction, true,
 DEFINE_bool(cleanup_code_caches_at_gc, true,
             "Flush inline caches prior to mark compact collection and "
             "flush code caches in maps during mark compact cycle.")
+DEFINE_bool(use_marking_progress_bar, false,
+            "Use a progress bar to scan large objects in increments when "
+            "incremental marking is active.")
 DEFINE_int(random_seed, 0,
            "Default seed for initializing random generator "
            "(0, the default, means to use system random).")