Before write-protecting a PageSpace, return bump allocation block to freelist.

runtime/vm/heap_test.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 "platform/globals.h"
 
 #include "platform/assert.h"
 #include "vm/dart_api_impl.h"
 #include "vm/globals.h"
 #include "vm/heap.h"
@@ skipping 234 matching lines @@
       EXPECT(obj.raw() == heap->FindObject(&find_only));
     }
   }
   {
     NoSafepointScope no_safepoint;
     FindNothing find_nothing;
     EXPECT(Object::null() == heap->FindObject(&find_nothing));
   }
 }
 
+
+TEST_CASE(IterateReadOnly) {
+  const String& obj = String::Handle(String::New("x", Heap::kOld));
+  Heap* heap = Thread::Current()->isolate()->heap();
+  EXPECT(heap->Contains(RawObject::ToAddr(obj.raw())));
+  heap->WriteProtect(true);
+  EXPECT(heap->Contains(RawObject::ToAddr(obj.raw())));
+  heap->WriteProtect(false);
+  EXPECT(heap->Contains(RawObject::ToAddr(obj.raw())));
+}
+
 }  // namespace dart.