Revert r38116 because of crashes.

runtime/vm/assembler_ia32.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_ASSEMBLER_IA32_H_
 #define VM_ASSEMBLER_IA32_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_ia32.h directly; use assembler.h instead.
 #endif
@@ skipping 576 matching lines @@
   void shld(Register dst, Register src);
   void shld(const Address& operand, Register src);
   void shrd(Register dst, Register src);
   void shrd(const Address& dst, Register src);
 
   void negl(Register reg);
   void notl(Register reg);
 
   void bsrl(Register dst, Register src);
 
-  void bt(Register base, Register offset);
-
   void enter(const Immediate& imm);
   void leave();
 
   void ret();
   void ret(const Immediate& imm);
 
   // 'size' indicates size in bytes and must be in the range 1..8.
   void nop(int size = 1);
   void int3();
   void hlt();
@@ skipping 291 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_IA32_H_