Exclude all references into the VM isolate in heap snapshots.

runtime/vm/object_graph.cc

 // Copyright (c) 2014, 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/object_graph.h"
 
 #include "vm/dart.h"
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 473 matching lines @@
   stream->WriteUnsigned(addr / kObjectAlignment);
 }
 
 
 class WritePointerVisitor : public ObjectPointerVisitor {
  public:
   WritePointerVisitor(Isolate* isolate, WriteStream* stream)
       : ObjectPointerVisitor(isolate), stream_(stream), count_(0) {}
   virtual void VisitPointers(RawObject** first, RawObject** last) {
     for (RawObject** current = first; current <= last; ++current) {
-      if (!(*current)->IsHeapObject() || (*current == Object::null())) {
-        // Ignore smis and nulls for now.
+      RawObject* object = *current;
+      if (!object->IsHeapObject() || object->IsVMHeapObject()) {
+        // Ignore smis and objects in the VM isolate for now.
         // TODO(koda): To track which field each pointer corresponds to,
         // we'll need to encode which fields were omitted here.
         continue;
       }
-      WritePtr(*current, stream_);
+      WritePtr(object, stream_);
       ++count_;
     }
   }
 
   intptr_t count() const { return count_; }
 
  private:
   WriteStream* stream_;
   intptr_t count_;
 };
@@ skipping 53 matching lines @@
   {
     WritePointerVisitor ptr_writer(isolate(), stream);
     isolate()->IterateObjectPointers(&ptr_writer, false);
   }
   stream->WriteUnsigned(0);
   IterateObjects(&visitor);
   return visitor.count() + 1;  // + root
 }
 
 }  // namespace dart