Fix bug in prototype transitions cache clearing introduced by r8165.

Invalid loop nesting causes full cleanup of the prototype transitions cache on every GC.

R=ager@chromium.org

Review URL: http://codereview.chromium.org/7354020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8634 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mark-compact.cc

@@ -1661,6 +1661,7 @@ void MarkCompactCollector::ClearNonLiveTransitions() {
 
     // Clear dead prototype transitions.
     int number_of_transitions = map->NumberOfProtoTransitions();
+    if (number_of_transitions > 0) {
       FixedArray* prototype_transitions = map->unchecked_prototype_transitions();
       int new_number_of_transitions = 0;
       const int header = Map::kProtoTransitionHeaderSize;
@@ -1687,6 +1688,7 @@ void MarkCompactCollector::ClearNonLiveTransitions() {
           }
           new_number_of_transitions++;
         }
+      }
 
       // Fill slots that became free with undefined value.
       Object* undefined = heap()->raw_unchecked_undefined_value();