VM: Fix incorrect debug assertion.

runtime/vm/jit_optimizer.cc

Index: runtime/vm/jit_optimizer.cc
diff --git a/runtime/vm/jit_optimizer.cc b/runtime/vm/jit_optimizer.cc
index 3ae456168757fa44c30585cd0bbd065b170ee31f..edb252402d1dfb4be80644b7a711fbd41e6163ab 100644
--- a/runtime/vm/jit_optimizer.cc
+++ b/runtime/vm/jit_optimizer.cc
@@ -3118,7 +3118,7 @@ bool JitOptimizer::TryInlineInstanceSetter(InstanceCallInstr* instr,
     AddReceiverCheck(instr);
   }
   if (field.guarded_cid() != kDynamicCid) {
-    ASSERT(!FLAG_use_field_guards);
+    ASSERT(FLAG_use_field_guards);
     InsertBefore(instr,
                  new(Z) GuardFieldClassInstr(
                      new(Z) Value(instr->ArgumentAt(1)),
@@ -3129,7 +3129,7 @@ bool JitOptimizer::TryInlineInstanceSetter(InstanceCallInstr* instr,
   }
 
   if (field.needs_length_check()) {
-    ASSERT(!FLAG_use_field_guards);
+    ASSERT(FLAG_use_field_guards);
     InsertBefore(instr,
                  new(Z) GuardFieldLengthInstr(
                      new(Z) Value(instr->ArgumentAt(1)),