Eliminate RawObject::class_ field entirely.

runtime/vm/assembler_macros_x64.cc

Index: runtime/vm/assembler_macros_x64.cc
diff --git a/runtime/vm/assembler_macros_x64.cc b/runtime/vm/assembler_macros_x64.cc
index 3327c6d626f12797443ab3367cebf20748207405..b36e568e6d1c1629ddf3947999b5e3a64cbb7aa8 100644
--- a/runtime/vm/assembler_macros_x64.cc
+++ b/runtime/vm/assembler_macros_x64.cc
@@ -18,20 +18,12 @@ DECLARE_FLAG(bool, inline_alloc);
 // Static.
 void AssemblerMacros::TryAllocate(Assembler* assembler,
                                   const Class& cls,
-                                  Register class_reg,
                                   Label* failure,
                                   Register instance_reg) {
 #if defined(DEBUG)
   __ Untested("AssemblerMacros::TryAllocate");
-  Label ok;
-  __ LoadObject(instance_reg, cls);
-  __ cmpq(instance_reg, class_reg);
-  __ j(EQUAL, &ok, Assembler::kNearJump);
-  __ Stop("AssemblerMacros::TryAllocate, wrong arguments");
-  __ Bind(&ok);
 #endif
   ASSERT(failure != NULL);
-  ASSERT(class_reg != instance_reg);
   if (FLAG_inline_alloc) {
     Heap* heap = Isolate::Current()->heap();
     const intptr_t instance_size = cls.instance_size();
@@ -48,9 +40,6 @@ void AssemblerMacros::TryAllocate(Assembler* assembler,
     __ movq(Address(TMP, 0), instance_reg);
     ASSERT(instance_size >= kHeapObjectTag);
     __ subq(instance_reg, Immediate(instance_size - kHeapObjectTag));
-    __ StoreIntoObject(instance_reg,
-                       FieldAddress(instance_reg, Instance::class_offset()),
-                       class_reg);
     uword tags = 0;
     tags = RawObject::SizeTag::update(instance_size, tags);
     ASSERT(cls.id() != kIllegalObjectKind);