Make sure we don't accidentially serialize type feedback

src/type-feedback-vector.cc

Index: src/type-feedback-vector.cc
diff --git a/src/type-feedback-vector.cc b/src/type-feedback-vector.cc
index 45028b87879f7bbe2984179c111f586ce6f9025e..5154e2078fc4c960298f28a5041559ad32c4a4f4 100644
--- a/src/type-feedback-vector.cc
+++ b/src/type-feedback-vector.cc
@@ -207,6 +207,42 @@ void TypeFeedbackVector::ClearSlots(SharedFunctionInfo* shared) {
 }
 
 
+bool TypeFeedbackVector::IsCleared() {
+  int slots = Slots();
+  Isolate* isolate = GetIsolate();
+  Object* uninitialized_sentinel =
+      TypeFeedbackVector::RawUninitializedSentinel(isolate->heap());
+
+  for (int i = 0; i < slots; i++) {
+    FeedbackVectorSlot slot(i);
+    Object* obj = Get(slot);
+    if (obj->IsHeapObject()) {
+      InstanceType instance_type =
+          HeapObject::cast(obj)->map()->instance_type();
+      // AllocationSites are exempt from clearing. They don't store Maps
+      // or Code pointers which can cause memory leaks if not cleared
+      // regularly.
+      if (instance_type != ALLOCATION_SITE_TYPE) {
+        return false;
+      }
+    }
+  }
+
+  slots = ICSlots();
+  if (slots == 0) return true;
+
+  // Now check vector-based ICs.
+  for (int i = 0; i < slots; i++) {
+    FeedbackVectorICSlot slot(i);
+    Object* obj = Get(slot);
+    if (obj != uninitialized_sentinel) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
 Handle<FixedArray> FeedbackNexus::EnsureArrayOfSize(int length) {
   Isolate* isolate = GetIsolate();
   Handle<Object> feedback = handle(GetFeedback(), isolate);