Uses double load/store on arm64, enables tests.

runtime/vm/guard_field_test.cc

 // Copyright (c) 2013, 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.
 
-// TODO(zra): Remove when tests are ready to enable.
-#include "platform/globals.h"
-#if !defined(TARGET_ARCH_ARM64)
-
 #include "vm/dart_api_impl.h"
 #include "vm/dart_api_state.h"
 #include "vm/intermediate_language.h"
 #include "vm/object.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
 RawField* LookupField(Dart_Handle library, const char* class_name,
                       const char* field_name) {
@@ skipping 248 matching lines @@
   Dart_Handle result = Dart_Invoke(lib, NewString("main"), 0, NULL);
   EXPECT_VALID(result);
   Field& f3 = Field::ZoneHandle(LookupField(lib, "A", "f3"));
   const intptr_t no_length = Field::kNoFixedLength;
   EXPECT_EQ(no_length, f3.guarded_list_length());
   EXPECT_EQ(kTypedDataFloat32ArrayCid, f3.guarded_cid());
   EXPECT_EQ(false, f3.is_nullable());
 }
 
 }  // namespace dart
-
-#endif  // !defined(TARGET_ARCH_ARM64)