Initialize CompareOperation::combined_type to avoid crashes.

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 2020 matching lines @@
  protected:
   CompareOperation(Isolate* isolate,
                    Token::Value op,
                    Expression* left,
                    Expression* right,
                    int pos)
       : Expression(isolate),
         op_(op),
         left_(left),
         right_(right),
-        pos_(pos) {
+        pos_(pos),
+        combined_type_(Type::Null(), isolate) {
     ASSERT(Token::IsCompareOp(op));
   }
 
  private:
   Token::Value op_;
   Expression* left_;
   Expression* right_;
   int pos_;
 
   Handle<Type> combined_type_;
@@ skipping 1190 matching lines @@
  private:
   Isolate* isolate_;
   Zone* zone_;
   Visitor visitor_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_