VM: Use read-only handle Object::dynamic_type() where possible.

runtime/vm/constant_propagator.cc

 // Copyright (c) 2013, 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/constant_propagator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
 #include "vm/flow_graph_range_analysis.h"
@@ skipping 849 matching lines @@
 void ConstantPropagator::VisitInstantiateType(InstantiateTypeInstr* instr) {
   const Object& object =
       instr->instantiator()->definition()->constant_value();
   if (IsNonConstant(object)) {
     SetValue(instr, non_constant_);
     return;
   }
   if (IsConstant(object)) {
     if (instr->type().IsTypeParameter()) {
       if (object.IsNull()) {
-        SetValue(instr, Type::ZoneHandle(Z, Type::DynamicType()));
+        SetValue(instr, Object::dynamic_type());
         return;
       }
       // We could try to instantiate the type parameter and return it if no
       // malformed error is reported.
     }
     SetValue(instr, non_constant_);
   }
 }
 
 
@@ skipping 802 matching lines @@
   graph_->MergeBlocks();
   GrowableArray<BitVector*> dominance_frontier;
   graph_->ComputeDominators(&dominance_frontier);
 
   if (FLAG_trace_constant_propagation) {
     FlowGraphPrinter::PrintGraph("After CP", graph_);
   }
 }
 
 }  // namespace dart