VM: Separate precompilation-specific code, make flags const.

runtime/vm/flags.h

 // 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.
 
 #ifndef VM_FLAGS_H_
 #define VM_FLAGS_H_
 
 #include "platform/assert.h"
 #include "vm/flag_list.h"
 #include "vm/globals.h"
@@ skipping 103 matching lines @@
 #define RELEASE_FLAG_MARCO(name, product_value, type, default_value, comment)  \
   const type FLAG_##name = product_value;
 
 #else  // defined(PRODUCT)
 
 #define RELEASE_FLAG_MARCO(name, product_value, type, default_value, comment)  \
   extern type FLAG_##name;
 
 #endif  // defined(PRODUCT)
 
+#if defined(DART_PRECOMPILED_RUNTIME)

[Ivan Posva, 2016/02/19 01:07:49]

As discussed we need to have a way for a flag to be unchangeable even in
non-precompiled product.

[Florian Schneider, 2016/02/19 17:42:29]

Done.

+#define PRECOMPILE_FLAG_MARCO(name, pre_value, type, default_value, comment)   \
+  const type FLAG_##name = pre_value;
+
+#else  // defined(DART_PRECOMPILED_RUNTIME)
+#define PRECOMPILE_FLAG_MARCO(name, pre_value, type, default_value, comment)   \
+  extern type FLAG_##name;
+
+#endif  // defined(DART_PRECOMPILED_RUNTIME)
+
 // Now declare all flags here.
-FLAG_LIST(PRODUCT_FLAG_MARCO, RELEASE_FLAG_MARCO, DEBUG_FLAG_MARCO)
+FLAG_LIST(PRODUCT_FLAG_MARCO,
+          RELEASE_FLAG_MARCO,
+          DEBUG_FLAG_MARCO,
+          PRECOMPILE_FLAG_MARCO)
 
 #undef RELEASE_FLAG_MARCO
 #undef DEBUG_FLAG_MARCO
 #undef PRODUCT_FLAG_MARCO
+#undef PRECOMPILE_FLAG_MARCO
 
 }  // namespace dart
 
 #endif  // VM_FLAGS_H_