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

runtime/vm/flags.cc

Index: runtime/vm/flags.cc
diff --git a/runtime/vm/flags.cc b/runtime/vm/flags.cc
index a2a63f7991020b81f566ea290f2fcb00acbbd34c..7f48a0a5b4e20376420625fb47fbb83d3d8bd089 100644
--- a/runtime/vm/flags.cc
+++ b/runtime/vm/flags.cc
@@ -41,13 +41,28 @@ DEFINE_FLAG(bool, ignore_unrecognized_flags, false,
                                             comment);
 #endif  // defined(PRODUCT)
 
+#if defined(DART_PRECOMPILED_RUNTIME)
+// Nothing to be done for the product flag definitions.
+#define PRECOMPILE_FLAG_MARCO(name, product_value, type, default_value, comment)
+#else  // defined(DART_PRECOMPILED_RUNTIME)
+#define PRECOMPILE_FLAG_MARCO(name, product_value, type, default_value,        \
+                              comment)                                         \
+  type FLAG_##name = Flags::Register_##type(&FLAG_##name,                      \
+                                            #name,                             \
+                                            default_value,                     \
+                                            comment);
+#endif  // defined(DART_PRECOMPILED_RUNTIME)
+
 // Define all of the non-product 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
 
 bool Flags::initialized_ = false;