Fix code age assignment.

src/objects-inl.h

 // Copyright 2011 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 3307 matching lines @@
   return static_cast<BuiltinFunctionId>(Smi::cast(function_data())->value());
 }
 
 
 int SharedFunctionInfo::code_age() {
   return (compiler_hints() >> kCodeAgeShift) & kCodeAgeMask;
 }
 
 
 void SharedFunctionInfo::set_code_age(int code_age) {
-  set_compiler_hints(compiler_hints() |
+  int clear_mask = ~(kCodeAgeMask << kCodeAgeShift);
+  set_compiler_hints((compiler_hints() & clear_mask) |
                      ((code_age & kCodeAgeMask) << kCodeAgeShift));
 }
 
 
 bool SharedFunctionInfo::has_deoptimization_support() {
   Code* code = this->code();
   return code->kind() == Code::FUNCTION && code->has_deoptimization_support();
 }
 
 
@@ skipping 867 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_