Cache lookups at megamorphic call sites in optimized code.

runtime/vm/raw_object.cc

Index: runtime/vm/raw_object.cc
diff --git a/runtime/vm/raw_object.cc b/runtime/vm/raw_object.cc
index 021a82f3cb09bd73ffbda3897911cab2371da9f3..1e42c9a94a58f7d9fb536320f90c6082926fb652 100644
--- a/runtime/vm/raw_object.cc
+++ b/runtime/vm/raw_object.cc
@@ -545,6 +545,14 @@ intptr_t RawICData::VisitICDataPointers(RawICData* raw_obj,
 }
 
 
+intptr_t RawMegamorphicCache::VisitMegamorphicCachePointers(
+    RawMegamorphicCache* raw_obj,
+    ObjectPointerVisitor* visitor) {
+  visitor->VisitPointers(raw_obj->from(), raw_obj->to());
+  return MegamorphicCache::InstanceSize();
+}
+
+
 intptr_t RawSubtypeTestCache::VisitSubtypeTestCachePointers(
     RawSubtypeTestCache* raw_obj, ObjectPointerVisitor* visitor) {
   // Make sure that we got here with the tagged pointer as this.