Revert r38116 because of crashes.

runtime/vm/assembler_x64.cc

 // 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.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
@@ skipping 2116 matching lines @@
 }
 
 
 void Assembler::notq(Register reg) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitRegisterREX(reg, REX_W);
   EmitUint8(0xF7);
   EmitUint8(0xD0 | (reg & 7));
 }
 
-void Assembler::btq(Register base, Register offset) {
-  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
-  Operand operand(base);
-  EmitOperandREX(offset, operand, REX_W);
-  EmitUint8(0x0F);
-  EmitUint8(0xA3);
-  EmitOperand(offset & 7, operand);
-}
-
 
 void Assembler::enter(const Immediate& imm) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0xC8);
   ASSERT(imm.is_uint16());
   EmitUint8(imm.value() & 0xFF);
   EmitUint8((imm.value() >> 8) & 0xFF);
   EmitUint8(0x00);
 }
 
@@ skipping 1238 matching lines @@
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64