Fix more GC unsafe places

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index 24b1d310970092fca11af6a2af22a70061df2445..53773acaf5fa04b16a22a3f731bb632b27369cc8 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -1034,10 +1034,12 @@ bool Debug::CheckBreakPoint(Handle<Object> break_point_object) {
   if (!break_point_object->IsJSObject()) return true;
 
   // Get the function CheckBreakPoint (defined in debug.js).
+  Handle<String> is_break_point_triggered_symbol =
+      Factory::LookupAsciiSymbol("IsBreakPointTriggered");
   Handle<JSFunction> check_break_point =
     Handle<JSFunction>(JSFunction::cast(
-      debug_context()->global()->GetProperty(
-          *Factory::LookupAsciiSymbol("IsBreakPointTriggered"))));
+        debug_context()->global()->GetProperty(
+            *is_break_point_triggered_symbol)));
 
   // Get the break id as an object.
   Handle<Object> break_id = Factory::NewNumberFromInt(Debug::break_id());
@@ -2176,9 +2178,11 @@ void Debugger::OnAfterCompile(Handle<Script> script,
   // script. Make sure that these break points are set.
 
   // Get the function UpdateScriptBreakPoints (defined in debug-debugger.js).
+  Handle<String> update_script_break_points_symbol =
+      Factory::LookupAsciiSymbol("UpdateScriptBreakPoints");
   Handle<Object> update_script_break_points =
       Handle<Object>(Debug::debug_context()->global()->GetProperty(
-          *Factory::LookupAsciiSymbol("UpdateScriptBreakPoints")));
+          *update_script_break_points_symbol));
   if (!update_script_break_points->IsJSFunction()) {
     return;
   }