(Experimental) Add Brooks pointers.

This feature is disabled by default.

Verified that the Brooks pointers are installed correctly by using the
CMS/SS collectors.

Change-Id: Ia9be9814ab6e29169ac85edc4792ce8c81d552a9
diff --git a/runtime/gc/space/space_test.h b/runtime/gc/space/space_test.h
index 093967e..41077f3 100644
--- a/runtime/gc/space/space_test.h
+++ b/runtime/gc/space/space_test.h
@@ -49,6 +49,9 @@
                                                                                       null_loader);
     EXPECT_TRUE(byte_array_class != nullptr);
     o->SetClass(byte_array_class);
+    if (kUseBrooksPointer) {
+      o->SetBrooksPointer(o.get());
+    }
     mirror::Array* arr = o->AsArray<kVerifyNone>();
     size_t header_size = SizeOfZeroLengthByteArray();
     int32_t length = size - header_size;