Simplify AST by extending LetNode and replace CommaNode.

runtime/vm/flow_graph_builder.h

 // 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.
 
 #ifndef VM_FLOW_GRAPH_BUILDER_H_
 #define VM_FLOW_GRAPH_BUILDER_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 400 matching lines @@
   virtual void VisitLoadLocalNode(LoadLocalNode* node);
   virtual void VisitStoreLocalNode(StoreLocalNode* node);
   virtual void VisitStoreIndexedNode(StoreIndexedNode* node);
   virtual void VisitStoreInstanceFieldNode(StoreInstanceFieldNode* node);
   virtual void VisitInstanceSetterNode(InstanceSetterNode* node);
   virtual void VisitThrowNode(ThrowNode* node);
   virtual void VisitClosureCallNode(ClosureCallNode* node);
   virtual void VisitStaticSetterNode(StaticSetterNode* node);
   virtual void VisitStoreStaticFieldNode(StoreStaticFieldNode* node);
   virtual void VisitTypeNode(TypeNode* node);
-  virtual void VisitCommaNode(CommaNode* node);
   virtual void VisitLetNode(LetNode* node);
 
   Value* value() const { return value_; }
 
  protected:
   // Output parameters.
   Value* value_;
 
  private:
   // Helper to set the output state to return a Value.
@@ skipping 70 matching lines @@
   // Output parameters.
   GrowableArray<TargetEntryInstr**> true_successor_addresses_;
   GrowableArray<TargetEntryInstr**> false_successor_addresses_;
 
   intptr_t condition_token_pos_;
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_BUILDER_H_