Move megamorphic cache table into the Dart heap.

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 0c992e107299e90b5e28aabe6b28ebb5fd0192bd..97a41c33aea6ea99a9b1c72733125f514e69d830 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -656,6 +656,7 @@ Isolate::Isolate(const Dart_IsolateFlags& api_flags)
   :   vm_tag_(0),
       store_buffer_(new StoreBuffer()),
       thread_registry_(new ThreadRegistry()),
+      megamorphic_cache_table_(this),
       message_notify_callback_(NULL),
       name_(NULL),
       debugger_name_(NULL),
@@ -1623,9 +1624,6 @@ void Isolate::VisitObjectPointers(ObjectPointerVisitor* visitor,
   // Visit objects in the class table.
   class_table()->VisitObjectPointers(visitor);
 
-  // Visit objects in the megamorphic cache.
-  megamorphic_cache_table()->VisitObjectPointers(visitor);
-
   // Visit objects in per isolate stubs.
   StubCode::VisitObjectPointers(visitor);