Set the default value for use_corelib_source_files to true on windows as we do not have the source …

runtime/vm/bootstrap.cc

 // Copyright (c) 2012, 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/bootstrap.h"
 
 #include "include/dart_api.h"
 
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart_api_impl.h"
 #if !defined(DART_PRECOMPILED_RUNTIME)
 #include "vm/kernel.h"
 #include "vm/kernel_reader.h"
 #endif
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/symbols.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool,
             use_corelib_source_files,
-            false,
+            kDefaultCorelibSourceFlag,
             "Attempt to use source files directly when loading in the core "
             "libraries during the bootstrap process");
 
 struct BootstrapLibProps {
   ObjectStore::BootstrapLibraryId index;
   const char* uri;
   const char** source_paths;
   const char* patch_uri;
   const char** patch_paths;
 };
@@ skipping 357 matching lines @@
       lib.Register(thread);
       isolate->object_store()->set_bootstrap_library(id, lib);
     }
   }
 
   return (kernel_program == NULL) ? BootstrapFromSource(thread)
                                   : BootstrapFromKernel(thread, kernel_program);
 }
 
 }  // namespace dart