VM: Allow configuring use_field_guards on the per-isolate basis and include it into snapshot featur…

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index 50e080967ae4efd51dffcaeda5556b5f5aee60c9..1aa4347233a9947f3dd1f1f19e1f1d6433ebee74 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -1084,7 +1084,7 @@ bool FlowGraphCompiler::TryIntrinsify() {
       if (field.is_instance() &&
           (FLAG_precompiled_mode || !IsPotentialUnboxedField(field))) {
         GenerateInlinedGetter(field.Offset());
-        return !FLAG_use_field_guards;
+        return !isolate()->use_field_guards();
       }
       return false;
     }
@@ -1097,7 +1097,7 @@ bool FlowGraphCompiler::TryIntrinsify() {
       if (field.is_instance() &&
           (FLAG_precompiled_mode || field.guarded_cid() == kDynamicCid)) {
         GenerateInlinedSetter(field.Offset());
-        return !FLAG_use_field_guards;
+        return !isolate()->use_field_guards();
       }
       return false;
     }