Fix dartium build break.

runtime/bin/gen_snapshot.cc

Index: runtime/bin/gen_snapshot.cc
===================================================================
--- runtime/bin/gen_snapshot.cc	(revision 38471)
+++ runtime/bin/gen_snapshot.cc	(working copy)
@@ -540,6 +540,16 @@
         Builtin::LoadAndCheckLibrary(Builtin::kBuiltinLibrary);
     CHECK_RESULT(builtin_lib);
 
+    // Ensure that we mark all libraries as loaded.
+    Dart_Handle result = Dart_FinalizeLoading(false);
+    if (Dart_IsError(result)) {
+      const char* err_msg = Dart_GetError(library);
+      Log::PrintErr("Errors encountered while loading: %s\n", err_msg);
+      Dart_ExitScope();
+      Dart_ShutdownIsolate();
+      exit(255);
+    }
+
     // Prepare for script loading by setting up the 'print' and 'timer'
     // closures and setting up 'package root' for URI resolution.
     result = DartUtils::PrepareForScriptLoading(package_root, builtin_lib);