Eliminate RawObject::class_ field entirely.

runtime/vm/assembler_macros_ia32.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.
 // The class 'AssemblerMacros' contains assembler instruction groups that
 // are used in Dart.
 
 #ifndef VM_ASSEMBLER_MACROS_IA32_H_
 #define VM_ASSEMBLER_MACROS_IA32_H_
 
 #ifndef VM_ASSEMBLER_MACROS_H_
 #error Do not include assembler_macros_ia32.h directly; use assembler_macros.h.
 #endif
 
 #include "vm/allocation.h"
 #include "vm/constants_ia32.h"
 
 namespace dart {
 
 // Forward declarations.
 class Assembler;
 class Class;
 class Label;
 
 class AssemblerMacros : public AllStatic {
  public:
   // Inlined allocation of an instance of class 'cls', code has no runtime
   // calls. Jump to 'failure' if the instance cannot be allocated here.
-  // Class must be loaded in 'class_reg'. Allocated instance is returned
-  // in 'instance_reg'. Only the class field of the object is initialized.
-  // 'class_reg' and 'instance_reg' may not be the same register.
+  // Allocated instance is returned in 'instance_reg'.
+  // Only the tags field of the object is initialized.
   static void TryAllocate(Assembler* assembler,
                           const Class& cls,
-                          Register class_reg,
                           Label* failure,
                           Register instance_reg);
 
   // Set up a dart frame on entry with a frame pointer and PC information to
   // enable easy access to the RawInstruction object of code corresponding
   // to this frame.
   // The dart frame layout is as follows:
   //   ....
   //   ret PC
   //   saved EBP     <=== EBP
@@ skipping 30 matching lines @@
   //   pushl ebp          (size is 1 byte)
   //   movl ebp, esp      (size is 2 bytes)
   //   call L             (size is 5 bytes)
   //   L:
   static const intptr_t kOffsetOfSavedPCfromEntrypoint = 8;
 };
 
 }  // namespace dart.
 
 #endif  // VM_ASSEMBLER_MACROS_IA32_H_