Use off-heap data for class check instructions

runtime/vm/flow_graph_type_propagator.cc

Index: runtime/vm/flow_graph_type_propagator.cc
diff --git a/runtime/vm/flow_graph_type_propagator.cc b/runtime/vm/flow_graph_type_propagator.cc
index 9617c03b3480e0c38da4ba21e4a48e71c1708757..13e31a181d7b7ac8551502c286c4d637f6bf2ff5 100644
--- a/runtime/vm/flow_graph_type_propagator.cc
+++ b/runtime/vm/flow_graph_type_propagator.cc
@@ -226,15 +226,18 @@ void FlowGraphTypePropagator::VisitCheckArrayBound(
 
 
 void FlowGraphTypePropagator::VisitCheckClass(CheckClassInstr* check) {
-  if (!check->unary_checks().NumberOfChecksIs(1) ||
-      !check->Dependencies().IsNone()) {
+  if (!check->targets().IsMonomorphic()) {
+    return;
+  }
+
+  if (!check->Dependencies().IsNone()) {
     // TODO(vegorov): If check is affected by side-effect we can still propagate
     // the type further but not the cid.
     return;
   }
 
   SetCid(check->value()->definition(),
-         check->unary_checks().GetReceiverClassIdAt(0));
+         check->targets().MonomorphicReceiverCid());
 }
 
 
@@ -473,7 +476,7 @@ void FlowGraphTypePropagator::StrengthenAssertWith(Instruction* check) {
     ASSERT(check->IsCheckClass());
     check_clone = new CheckClassInstr(
         assert->value()->Copy(zone()), assert->env()->deopt_id(),
-        check->AsCheckClass()->unary_checks(), check->token_pos());
+        check->AsCheckClass()->targets(), check->token_pos());
     check_clone->AsCheckClass()->set_licm_hoisted(
         check->AsCheckClass()->licm_hoisted());
   }