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

runtime/vm/kernel_isolate.cc

 // Copyright (c) 2016, 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/kernel_isolate.h"
 
 #include "vm/compiler.h"
 #include "include/dart_native_api.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
@@ skipping 50 matching lines @@
     Isolate* isolate = NULL;
 
     Dart_IsolateCreateCallback create_callback =
         KernelIsolate::create_callback();
 
     if (create_callback == NULL) {
       KernelIsolate::FinishedInitializing();
       return;
     }
 
+    // Note: these flags must match those passed to the VM during
+    // the app-jit training run (see //utils/kernel-service/BUILD.gn).
     Dart_IsolateFlags api_flags;
     api_flags.version = DART_FLAGS_CURRENT_VERSION;
     api_flags.enable_type_checks = false;
     api_flags.enable_asserts = false;
     api_flags.enable_error_on_bad_type = false;
     api_flags.enable_error_on_bad_override = false;
+    api_flags.use_field_guards = true;
 
     isolate = reinterpret_cast<Isolate*>(create_callback(
         KernelIsolate::kName, NULL, NULL, NULL, &api_flags, NULL, &error));
     if (isolate == NULL) {
       OS::PrintErr(DART_KERNEL_ISOLATE_NAME ": Isolate creation error: %s\n",
                    error);
       KernelIsolate::SetKernelIsolate(NULL);
       KernelIsolate::FinishedInitializing();
       return;
     }
@@ skipping 350 matching lines @@
   }
 
   KernelCompilationRequest request;
   return request.SendAndWaitForResponse(kernel_port, script_uri);
 }
 
 
 #endif  // DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart