Fix cctest + unittest to work with an external snapshot.

src/startup-data-util.h

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+
+#ifndef V8_STARTUP_DATA_UTIL_H_
+#define V8_STARTUP_DATA_UTIL_H_
+
+#include "include/v8.h"
+
+namespace v8 {
+
+#ifdef V8_USE_EXTERNAL_STARTUP_DATA
+// Helper class to load the startup data files from disk.
+//
+// This is meant as a convenience for stand-alone binaries like d8, cctest,
+// unittest. A V8 embedder would likely either handle startup data on their
+// own or just disable the feature if they don't want to handle it at all,
+// while tools like cctest need to work in either configuration. Hence this is
+// not meant for inclusion in the general v8 library.
+class StartupDataHandler {
+ public:
+  // Load startup data, and call the v8::V8::Set*DataBlob API functions.
+  //
+  // natives_blob and snapshot_blob will be loaded realitive to exec_path,
+  // which would usually be the equivalent of argv[0].
+  StartupDataHandler(const char* exec_path, const char* natives_blob,
+                     const char* snapshot_blob);
+  ~StartupDataHandler();
+
+ private:
+  static char* RelativePath(char** buffer, const char* exec_path,
+                            const char* name);
+
+  void LoadFromFiles(const char* natives_blob, const char* snapshot_blob);
+
+  void Load(const char* blob_file, v8::StartupData* startup_data,
+            void (*setter_fn)(v8::StartupData*));
+
+  v8::StartupData natives_;
+  v8::StartupData snapshot_;
+
+  // Disallow copy & assign.
+  StartupDataHandler(const StartupDataHandler& other);
+  void operator=(const StartupDataHandler& other);
+};
+#endif  // V8_USE_EXTERNAL_STARTUP_DATA
+
+}  // namespace v8
+
+#endif  // V8_STARTUP_DATA_UTIL_H_