Turn off background compilation when running with --verify_gc, since the background compilation con…

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 602ea500fefb9c3ca58d61c55b640d2d19b1e834..a78cc8b9c48df2a1167305645c615b2bab048b0f 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -15515,6 +15515,10 @@ TokenPosition AbstractType::token_pos() const {
 
 bool AbstractType::IsInstantiated(TrailPtr trail) const {
   // AbstractType is an abstract class.
+  // TODO(srdjan) : Remove temporary code.
+  if (Compiler::IsBackgroundCompilation()) {
+    UNREACHABLE();
+  }
   UNREACHABLE();
   return false;
 }