Add a -verbose:thread option.

Change-Id: Ie9bbe2195d7c427379e4a27d3fe51f1a71e58597
diff --git a/src/runtime.cc b/src/runtime.cc
index 424b6f7..acb42e9 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -405,7 +405,7 @@
 
   default_stack_size_ = options->stack_size_;
 
-  thread_list_ = new ThreadList;
+  thread_list_ = new ThreadList(options->IsVerbose("thread"));
   intern_table_ = new InternTable;
 
   Heap::Init(options->heap_initial_size_, options->heap_maximum_size_,