Annotate PromotionQueue::RelocateQueueHead for MemorySanitizer.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 1cc646e14465620e244101a2470d45dfa23193fa..fc538530c328705126e65b259b5c60aeb401fc47 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1383,6 +1383,10 @@ void PromotionQueue::RelocateQueueHead() {
   while (head_start != head_end) {
     int size = static_cast<int>(*(head_start++));
     HeapObject* obj = reinterpret_cast<HeapObject*>(*(head_start++));
+    // New space allocation in SemiSpaceCopyObject marked the region
+    // overlapping with promotion queue as uninitialized.
+    MSAN_MEMORY_IS_INITIALIZED(&size, sizeof(size));
+    MSAN_MEMORY_IS_INITIALIZED(&obj, sizeof(obj));
     emergency_stack_->Add(Entry(obj, size));
   }
   rear_ = head_end;