Regularize some naming to make BUILD.gn files easier to write.

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
===================================================================
--- runtime/vm/dart.cc	(revision 41495)
+++ runtime/vm/dart.cc	(working copy)
@@ -80,7 +80,7 @@
                            Dart_ServiceIsolateCreateCalback service_create) {
   // TODO(iposva): Fix race condition here.
   if (vm_isolate_ != NULL || !Flags::Initialized()) {
-    return "VM already initialized.";
+    return "VM already initialized or flags not initialized.";
   }
   Isolate::SetFileCallbacks(file_open, file_read, file_write, file_close);
   Isolate::SetEntropySourceCallback(entropy_source);