Do not go to slow mode and back to fast in initializer blocks.

src/ast.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1852 matching lines @@
 
   Token::Value op() const { return op_; }
   Expression* target() const { return target_; }
   Expression* value() const { return value_; }
   virtual int position() const { return pos_; }
   BinaryOperation* binary_operation() const { return binary_operation_; }
 
   // This check relies on the definition order of token in token.h.
   bool is_compound() const { return op() > Token::ASSIGN; }
 
-  // An initialization block is a series of statments of the form
-  // x.y.z.a = ...; x.y.z.b = ...; etc. The parser marks the beginning and
-  // ending of these blocks to allow for optimizations of initialization
-  // blocks.
-  bool starts_initialization_block() { return block_start_; }
-  bool ends_initialization_block() { return block_end_; }
-  void mark_block_start() { block_start_ = true; }
-  void mark_block_end() { block_end_ = true; }
-
   BailoutId AssignmentId() const { return assignment_id_; }
 
   // Type feedback information.
   TypeFeedbackId AssignmentFeedbackId() { return reuse(id()); }
   void RecordTypeFeedback(TypeFeedbackOracle* oracle, Zone* zone);
   virtual bool IsMonomorphic() { return is_monomorphic_; }
   virtual SmallMapList* GetReceiverTypes() { return &receiver_types_; }
 
  protected:
   Assignment(Isolate* isolate,
@@ skipping 12 matching lines @@
   }
 
  private:
   Token::Value op_;
   Expression* target_;
   Expression* value_;
   int pos_;
   BinaryOperation* binary_operation_;
   const BailoutId assignment_id_;
 
-  bool block_start_;
-  bool block_end_;
-
   bool is_monomorphic_;
   SmallMapList receiver_types_;
 };
 
 
 class Throw: public Expression {
  public:
   DECLARE_NODE_TYPE(Throw)
 
   Expression* exception() const { return exception_; }
@@ skipping 988 matching lines @@
  private:
   Isolate* isolate_;
   Zone* zone_;
   Visitor visitor_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_