Migrate most uses of StackZone(Isolate*) to Thread*.

runtime/vm/megamorphic_cache_table.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/megamorphic_cache_table.h"
 
 #include <stdlib.h>
 #include "vm/object.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
@@ skipping 70 matching lines @@
   v->VisitPointer(reinterpret_cast<RawObject**>(&miss_handler_function_));
   for (intptr_t i = 0; i < length_; ++i) {
     v->VisitPointer(reinterpret_cast<RawObject**>(&table_[i].name));
     v->VisitPointer(reinterpret_cast<RawObject**>(&table_[i].descriptor));
     v->VisitPointer(reinterpret_cast<RawObject**>(&table_[i].cache));
   }
 }
 
 
 void MegamorphicCacheTable::PrintSizes() {
-  StackZone zone(Isolate::Current());
+  StackZone zone(Thread::Current());
   intptr_t size = 0;
   MegamorphicCache& cache = MegamorphicCache::Handle();
   Array& buckets = Array::Handle();
   for (intptr_t i = 0; i < length_; ++i) {
     cache = table_[i].cache;
     buckets = cache.buckets();
     size += MegamorphicCache::InstanceSize();
     size += Array::InstanceSize(buckets.Length());
   }
   OS::Print("%" Pd " megamorphic caches using %" Pd "KB.\n",
             length_, size / 1024);
 }
 
 }  // namespace dart