Rework standalone to use a synchronous loader that does not invoke Dart code

runtime/bin/gen_snapshot.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.
 
 // Generate a snapshot file after loading all the scripts specified on the
 // command line.
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ skipping 580 matching lines @@
 static Dart_Handle LoadGenericSnapshotCreationScript(
     Builtin::BuiltinLibraryId id) {
   Dart_Handle source = Builtin::Source(id);
   if (Dart_IsError(source)) {
     return source;  // source contains the error string.
   }
   Dart_Handle lib;
   // Load the builtin library to make it available in the snapshot
   // for importing.
   lib = Builtin::LoadAndCheckLibrary(id);
+  if (Dart_IsError(lib)) {
+    fprintf(stderr, "%s", Dart_GetError(lib));

[turnidge, 2016/06/03 17:50:25]

Debug stuff....

[Cutch, 2016/06/03 22:07:32]

Done.

+  }
   ASSERT(!Dart_IsError(lib));
   return lib;
 }
 
 
 static void PrintUsage() {
   Log::PrintErr(
 "Usage:                                                                      \n"
 " gen_snapshot [<vm-flags>] [<options>] [<dart-script-file>]                 \n"
 "                                                                            \n"
@@ skipping 737 matching lines @@
   EventHandler::Stop();
   return 0;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   return dart::bin::main(argc, argv);
 }