Specialize mint shift code on ia32 for a constant shift amount.

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 568 matching lines @@
 
   void shll(Register reg, const Immediate& imm);
   void shll(Register operand, Register shifter);
   void shll(const Address& operand, Register shifter);
   void shrl(Register reg, const Immediate& imm);
   void shrl(Register operand, Register shifter);
   void sarl(Register reg, const Immediate& imm);
   void sarl(Register operand, Register shifter);
   void sarl(const Address& address, Register shifter);
   void shld(Register dst, Register src);
+  void shld(Register dst, Register src, const Immediate& imm);
   void shld(const Address& operand, Register src);
   void shrd(Register dst, Register src);
+  void shrd(Register dst, Register src, const Immediate& imm);
   void shrd(const Address& dst, Register src);
 
   void negl(Register reg);
   void notl(Register reg);
 
   void bsrl(Register dst, Register src);
 
   void enter(const Immediate& imm);
   void leave();
 
@@ skipping 298 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_IA32_H_