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

runtime/vm/flow_graph_compiler.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_XXX.
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
@@ skipping 1066 matching lines @@
       // TODO(27590) Store Field object inside RawFunction::data_ if possible.
       name = Field::NameFromGetter(name);
       const Field& field = Field::Handle(owner.LookupFieldAllowPrivate(name));
       ASSERT(!field.IsNull());
 
       // Only intrinsify getter if the field cannot contain a mutable double.
       // Reading from a mutable double box requires allocating a fresh double.
       if (field.is_instance() &&
           (FLAG_precompiled_mode || !IsPotentialUnboxedField(field))) {
         GenerateInlinedGetter(field.Offset());
-        return !FLAG_use_field_guards;
+        return !isolate()->use_field_guards();
       }
       return false;
     }
     if (parsed_function().function().kind() == RawFunction::kImplicitSetter) {
       // TODO(27590) Store Field object inside RawFunction::data_ if possible.
       name = Field::NameFromSetter(name);
       const Field& field = Field::Handle(owner.LookupFieldAllowPrivate(name));
       ASSERT(!field.IsNull());
 
       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;
     }
   }
 
   EnterIntrinsicMode();
 
   bool complete = Intrinsifier::Intrinsify(parsed_function(), this);
 
   ExitIntrinsicMode();
@@ skipping 775 matching lines @@
 
 
 void FlowGraphCompiler::FrameStateClear() {
   ASSERT(!is_optimizing());
   frame_state_.TruncateTo(0);
 }
 #endif  // defined(DEBUG) && !defined(TARGET_ARCH_DBC)
 
 
 }  // namespace dart