Optimize ClearNonLiveReferences: do not compact prototype transitions in GC.

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2603 matching lines @@
         global->Get(ctx, v8_str("g")).ToLocalChecked());
     g->Call(ctx, global, 0, nullptr).ToLocalChecked();
   }
 
   CcTest::heap()->incremental_marking()->set_should_hurry(true);
   CcTest::heap()->CollectGarbage(OLD_SPACE);
 }
 
 
 static int NumberOfProtoTransitions(Map* map) {
-  return TransitionArray::NumberOfPrototypeTransitions(
-      TransitionArray::GetPrototypeTransitions(map));
+  FixedArray* transitions = TransitionArray::GetPrototypeTransitions(map);
+  TransitionArray::CompactPrototypeTransitionArray(transitions);
+  return TransitionArray::NumberOfPrototypeTransitions(transitions);
 }
 
 
 TEST(PrototypeTransitionClearing) {
   if (FLAG_never_compact) return;
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   Factory* factory = isolate->factory();
   v8::HandleScope scope(CcTest::isolate());
   v8::Local<v8::Context> ctx = CcTest::isolate()->GetCurrentContext();
@@ skipping 3813 matching lines @@
   isolate->IncrementJsCallsFromApiCounter();
   isolate->IncrementJsCallsFromApiCounter();
   isolate->IncrementJsCallsFromApiCounter();
   calls_per_ms = memory_reducer->SampleAndGetJsCallsPerMs(4);
   CheckDoubleEquals(2, calls_per_ms);
 }
 
 
 }  // namespace internal
 }  // namespace v8