Make subtype test stubs isolate-specific.

runtime/vm/assembler_ia32.cc

Index: runtime/vm/assembler_ia32.cc
===================================================================
--- runtime/vm/assembler_ia32.cc	(revision 40703)
+++ runtime/vm/assembler_ia32.cc	(working copy)
@@ -2736,27 +2736,22 @@
 }
 
 
-void Assembler::LoadClassById(Register result, Register class_id) {
+void Assembler::LoadClassById(Register result,
+                              Register class_id,
+                              Isolate* isolate) {
   ASSERT(result != class_id);
-  movl(result, FieldAddress(CTX, Context::isolate_offset()));
-  const intptr_t table_offset_in_isolate =
-      Isolate::class_table_offset() + ClassTable::table_offset();
-  movl(result, Address(result, table_offset_in_isolate));
+  movl(result, Address::Absolute(isolate->ClassTableAddress()));
   movl(result, Address(result, class_id, TIMES_4, 0));
 }
 
 
 void Assembler::LoadClass(Register result,
                           Register object,
-                          Register scratch) {
+                          Register scratch,
+                          Isolate* isolate) {
   ASSERT(scratch != result);
   LoadClassId(scratch, object);
-
-  movl(result, FieldAddress(CTX, Context::isolate_offset()));
-  const intptr_t table_offset_in_isolate =
-      Isolate::class_table_offset() + ClassTable::table_offset();
-  movl(result, Address(result, table_offset_in_isolate));
-  movl(result, Address(result, scratch, TIMES_4, 0));
+  LoadClassById(result, scratch, isolate);
 }