[Bindings] Create and use V8 context snapshots

tools/v8_context_snapshot/v8_context_snapshot_generator.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/at_exit.h"
+#include "base/command_line.h"
+#include "base/files/file_util.h"
+#include "base/message_loop/message_loop.h"
+#include "base/task_scheduler/task_scheduler.h"
+#include "gin/v8_initializer.h"
+#include "mojo/edk/embedder/embedder.h"
+#include "third_party/WebKit/public/platform/WebThread.h"
+#include "third_party/WebKit/public/web/WebKit.h"
+#include "third_party/WebKit/public/web/WebV8ContextSnapshot.h"
+#include "v8/include/v8.h"
+
+namespace {
+
+class SnapshotThread : public blink::WebThread {
+ public:
+  bool IsCurrentThread() const override { return true; }
+  blink::WebScheduler* Scheduler() const override { return nullptr; }
+  blink::WebTaskRunner* GetWebTaskRunner() override { return nullptr; }
+};
+
+class SnapshotPlatform final : public blink::Platform {
+ public:
+  bool IsTakingV8ContextSnapshot() override { return true; }
+  blink::WebThread* CurrentThread() override {
+    static SnapshotThread dummy_thread;
+    return &dummy_thread;
+  }
+};
+
+}  // namespace
+
+// This program takes a snapshot of V8 contexts and writes it out as a file.
+// The snapshot file is consumed by Blink.
+//
+// Usage:
+// % v8_context_snapshot_generator --output_file=<filename>
+int main(int argc, char** argv) {
+  base::AtExitManager at_exit;
+  base::CommandLine::Init(argc, argv);
+#ifdef V8_USE_EXTERNAL_STARTUP_DATA
+  gin::V8Initializer::LoadV8Snapshot();
+  gin::V8Initializer::LoadV8Natives();
+#endif
+
+  // Set up environment to make Blink and V8 workable.
+  base::MessageLoop message_loop;
+  base::TaskScheduler::CreateAndStartWithDefaultParams("TakeSnapshot");
+  mojo::edk::Init();
+
+  // Take a snapshot.
+  SnapshotPlatform platform;
+  blink::Initialize(&platform);
+  v8::StartupData blob = blink::WebV8ContextSnapshot::TakeSnapshot();
+
+  // Save the snapshot as a file. Filename is given in a command line option.
+  base::FilePath file_path =
+      base::CommandLine::ForCurrentProcess()->GetSwitchValuePath("output_file");
+  CHECK(!file_path.empty());
+  CHECK_LT(0, base::WriteFile(file_path, blob.data, blob.raw_size));
+
+  delete[] blob.data;
+
+  return 0;
+}