Factor out snapshot helpers from main.cc.

runtime/bin/error_exit.h

+// Copyright (c) 2017, 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 RUNTIME_BIN_ERROR_EXIT_H_
+#define RUNTIME_BIN_ERROR_EXIT_H_
+
+namespace dart {
+namespace bin {
+
+// Exit code indicating an internal Dart Frontend error.
+static const int kDartFrontendErrorExitCode = 252;
+// Exit code indicating an API error.
+static const int kApiErrorExitCode = 253;
+// Exit code indicating a compilation error.
+static const int kCompilationErrorExitCode = 254;
+// Exit code indicating an unhandled error that is not a compilation error.
+static const int kErrorExitCode = 255;
+// Exit code indicating a vm restart request.  Never returned to the user.
+static const int kRestartRequestExitCode = 1000;
+
+void ErrorExit(int exit_code, const char* format, ...);
+
+}  // namespace bin
+}  // namespace dart
+
+#endif  // RUNTIME_BIN_ERROR_EXIT_H_