Begins work on ARM64, first assembler test.

runtime/vm/code_descriptors_test.cc

Index: runtime/vm/code_descriptors_test.cc
===================================================================
--- runtime/vm/code_descriptors_test.cc	(revision 34648)
+++ runtime/vm/code_descriptors_test.cc	(working copy)
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(zra): Remove when tests are ready to enable.
+#include "platform/globals.h"
+#if !defined(TARGET_ARCH_ARM64)
+
 #include "platform/assert.h"
 #include "vm/globals.h"
 
@@ -280,3 +284,5 @@
 }
 
 }  // namespace dart
+
+#endif  // !defined(TARGET_ARCH_ARM64)