VM: Normalize function result type void to null in the flow graph.

runtime/vm/intermediate_language.h

 // 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.
 
 #ifndef VM_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 2462 matching lines @@
         dst_type_(AbstractType::ZoneHandle(dst_type.raw())),
         dst_name_(dst_name) {
     ASSERT(!dst_type.IsNull());
     ASSERT(!dst_name.IsNull());
     SetInputAt(0, value);
     SetInputAt(1, instantiator);
     SetInputAt(2, instantiator_type_arguments);
   }
 
   DECLARE_INSTRUCTION(AssertAssignable)
-  virtual CompileType* ComputeInitialType() const;
+  virtual CompileType ComputeType() const;
   virtual bool RecomputeType();
 
   Value* value() const { return inputs_[0]; }
   Value* instantiator() const { return inputs_[1]; }
   Value* instantiator_type_arguments() const { return inputs_[2]; }
 
   virtual intptr_t token_pos() const { return token_pos_; }
   const AbstractType& dst_type() const { return dst_type_; }
   void set_dst_type(const AbstractType& dst_type) {
     dst_type_ = dst_type.raw();
@@ skipping 5274 matching lines @@
       Isolate* isolate, bool opt) const {                                     \
     UNIMPLEMENTED();                                                          \
     return NULL;                                                              \
   }                                                                           \
   void Name::EmitNativeCode(FlowGraphCompiler* compiler) { UNIMPLEMENTED(); }
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_