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

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 8bc07769b532db7e1b553235c51fc1ef7d04a4a1..ac9db2d3b469558732d79922c926ffcdc0521a89 100644
--- a/runtime/vm/jit_optimizer.cc
+++ b/runtime/vm/jit_optimizer.cc
@@ -1805,7 +1805,7 @@ bool JitOptimizer::TryInlineInstanceSetter(InstanceCallInstr* instr,
     AddReceiverCheck(instr);
   }
   if (field.guarded_cid() != kDynamicCid) {
-    ASSERT(FLAG_use_field_guards);
+    ASSERT(I->use_field_guards());
     InsertBefore(
         instr, new (Z) GuardFieldClassInstr(new (Z) Value(instr->ArgumentAt(1)),
                                             field, instr->deopt_id()),
@@ -1813,7 +1813,7 @@ bool JitOptimizer::TryInlineInstanceSetter(InstanceCallInstr* instr,
   }
 
   if (field.needs_length_check()) {
-    ASSERT(FLAG_use_field_guards);
+    ASSERT(I->use_field_guards());
     InsertBefore(instr, new (Z) GuardFieldLengthInstr(
                             new (Z) Value(instr->ArgumentAt(1)), field,
                             instr->deopt_id()),