Introduce instance type for transition arrays.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 8d4921f8d15e39d33d803866ee9d6d827176d2c6..d1e233a36a780433ded4f259d3d68a30236b22d9 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -831,6 +831,7 @@ void MarkCompactCollector::Prepare() {
     ClearMarkbits();
     AbortWeakCollections();
     AbortWeakCells();
+    AbortTransitionArrays();
     AbortCompaction();
     was_marked_incrementally_ = false;
   }
@@ -2329,14 +2330,15 @@ void MarkCompactCollector::ProcessWeakReferences() {
   ClearNonLiveReferences();
 
   ClearWeakCollections();
-
-  heap_->set_encountered_weak_cells(Smi::FromInt(0));
 }
 
 
 void MarkCompactCollector::ClearNonLiveReferences() {
   GCTracer::Scope gc_scope(heap()->tracer(),
                            GCTracer::Scope::MC_NONLIVEREFERENCES);
+
+  ProcessAndClearTransitionArrays();
+
   // Iterate over the map space, setting map transitions that go from
   // a marked map to an unmarked map to null transitions.  This action
   // is carried out only on maps of JSObjects and related subtypes.
@@ -2655,6 +2657,31 @@ void MarkCompactCollector::AbortWeakCells() {
 }
 
 
+void MarkCompactCollector::ProcessAndClearTransitionArrays() {
+  HeapObject* undefined = heap()->undefined_value();
+  Object* obj = heap()->encountered_transition_arrays();
+  while (obj != Smi::FromInt(0)) {
+    TransitionArray* array = TransitionArray::cast(obj);
+    // TODO(ulan): move logic from ClearMapTransitions here.
+    obj = array->next_link();
+    array->set_next_link(undefined, SKIP_WRITE_BARRIER);
+  }
+  heap()->set_encountered_transition_arrays(Smi::FromInt(0));
+}
+
+
+void MarkCompactCollector::AbortTransitionArrays() {
+  HeapObject* undefined = heap()->undefined_value();
+  Object* obj = heap()->encountered_transition_arrays();
+  while (obj != Smi::FromInt(0)) {
+    TransitionArray* array = TransitionArray::cast(obj);
+    obj = array->next_link();
+    array->set_next_link(undefined, SKIP_WRITE_BARRIER);
+  }
+  heap()->set_encountered_transition_arrays(Smi::FromInt(0));
+}
+
+
 void MarkCompactCollector::RecordMigratedSlot(
     Object* value, Address slot, SlotsBuffer** evacuation_slots_buffer) {
   // When parallel compaction is in progress, store and slots buffer entries