Port code generator to x64.

runtime/vm/constants_x64.h

 // Copyright (c) 2011, 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_CONSTANTS_X64_H_
 #define VM_CONSTANTS_X64_H_
 
 namespace dart {
 
 enum Register {
@@ skipping 117 matching lines @@
   // to allocate or create instances of class Instr.
   // Use the At(pc) function to create references to Instr.
   static Instr* At(uword pc) { return reinterpret_cast<Instr*>(pc); }
 
  private:
   DISALLOW_ALLOCATION();
   // We need to prevent the creation of instances of class Instr.
   DISALLOW_IMPLICIT_CONSTRUCTORS(Instr);
 };
 
+
+// The largest multibyte nop we will emit.  This could go up to 15 if it
+// becomes important to us.
+const int MAX_NOP_SIZE = 8;
+
 }  // namespace dart
 
 #endif  // VM_CONSTANTS_X64_H_