Fix uninitialized field in Debug::ThreadInit().

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index 58098547252d160f8b6d0d5632840b8ee37701e5..1234196ab6182e1d1b488de856717bbf2f35eed7 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -551,6 +551,7 @@ void Debug::ThreadInit() {
   thread_local_.after_break_target_ = 0;
   thread_local_.debugger_entry_ = NULL;
   thread_local_.pending_interrupts_ = 0;
+  thread_local_.restarter_frame_function_pointer_ = NULL;
 }