Optimize ClearNonLiveReferences: do not compact prototype transitions in GC.

test/cctest/test-heap.cc

Index: test/cctest/test-heap.cc
diff --git a/test/cctest/test-heap.cc b/test/cctest/test-heap.cc
index c7625888b1103fc9640db86771534046d636f9f1..e995a687244f5f305ac616d9cd65dc6bfaf133ec 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -2621,8 +2621,9 @@ TEST(InstanceOfStubWriteBarrier) {
 
 
 static int NumberOfProtoTransitions(Map* map) {
-  return TransitionArray::NumberOfPrototypeTransitions(
-      TransitionArray::GetPrototypeTransitions(map));
+  FixedArray* transitions = TransitionArray::GetPrototypeTransitions(map);
+  TransitionArray::CompactPrototypeTransitionArray(transitions);
+  return TransitionArray::NumberOfPrototypeTransitions(transitions);
 }