Fix Flutter engine build

runtime/vm/dart.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/dart.h"
 
 #include "vm/become.h"
 #include "vm/clustered_snapshot.h"
 #include "vm/code_observers.h"
 #include "vm/cpu.h"
@@ skipping 587 matching lines @@
   }
 
   I->heap()->InitGrowthControl();
   I->set_init_callback_data(data);
   Api::SetupAcquiredError(I);
   if (FLAG_print_class_table) {
     I->class_table()->Print();
   }
 
   bool is_kernel_isolate = false;
+  USE(is_kernel_isolate);
+
 #ifndef DART_PRECOMPILED_RUNTIME
   KernelIsolate::InitCallback(I);
   is_kernel_isolate = KernelIsolate::IsKernelIsolate(I);
 #endif
+
   ServiceIsolate::MaybeMakeServiceIsolate(I);
 #if !defined(PRODUCT)
   if (!ServiceIsolate::IsServiceIsolate(I) && !is_kernel_isolate) {
     I->message_handler()->set_should_pause_on_start(
         FLAG_pause_isolates_on_start);
     I->message_handler()->set_should_pause_on_exit(FLAG_pause_isolates_on_exit);
   }
 #endif  // !defined(PRODUCT)
 
   ServiceIsolate::SendIsolateStartupMessage();
@@ skipping 124 matching lines @@
   ASSERT(predefined_handles_ != NULL);
   return predefined_handles_->handles_.IsValidScopedHandle(address);
 }
 
 bool Dart::IsReadOnlyApiHandle(Dart_Handle handle) {
   ASSERT(predefined_handles_ != NULL);
   return predefined_handles_->api_handles_.IsValidHandle(handle);
 }
 
 }  // namespace dart