[Bindings] Create and use V8 context snapshots

gin/shell/gin_prepare_main.cc

+// Copyright 2016 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/bind.h"
+#include "base/command_line.h"
+#include "base/files/file_util.h"
+#include "base/location.h"
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
+#include "base/single_thread_task_runner.h"
+#include "base/task_scheduler/task_scheduler.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "gin/array_buffer.h"
+#include "gin/modules/console.h"
+#include "gin/modules/module_runner_delegate.h"
+#include "gin/public/isolate_holder.h"
+#include "gin/try_catch.h"
+#include "gin/v8_initializer.h"
+#include "mojo/edk/embedder/embedder.h"
+#include "third_party/WebKit/public/web/SnapshotCreator.h"
+#include "third_party/WebKit/public/web/WebKit.h"
+#include "v8/include/v8.h"
+
+namespace gin {
+namespace {
+
+std::vector<base::FilePath> GetModuleSearchPaths() {
+  std::vector<base::FilePath> module_base(1);
+  CHECK(base::GetCurrentDirectory(&module_base[0]));
+  return module_base;
+}
+
+class GinShellRunnerDelegate final : public ModuleRunnerDelegate {
+ public:
+  GinShellRunnerDelegate() : ModuleRunnerDelegate(GetModuleSearchPaths()) {
+    AddBuiltinModule(Console::kModuleName, Console::GetModule);
+  }
+
+  void UnhandledException(ShellRunner* runner, TryCatch& try_catch) override {
+    ModuleRunnerDelegate::UnhandledException(runner, try_catch);
+    LOG(ERROR) << try_catch.GetStackTrace();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(GinShellRunnerDelegate);
+};
+
+class GinBlinkPlatform final : public blink::Platform {
+ public:
+  bool TakeV8Snapshot() override { return true; }
+};
+
+}  // namespace
+}  // namespace gin
+
+int main(int argc, char** argv) {

[Yuki, 2017/05/30 14:35:56]

Can you put a comment about the usage of this program?
What arguments are expected?  How to invoke this program?  What this program
does?

By the way, why is this named "gin_prepare_main.cc"?
"take_blink_v8_context_snapshot_main.cc" makes more sense to me. (I agree that
it's a little bit too long, though.)

[peria, 2017/06/01 08:33:32]

Done.

+  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.

[Yuki, 2017/05/30 14:35:56]

nit: s/set/Set/

[peria, 2017/06/01 08:33:32]

Done.

+  base::MessageLoop message_loop;
+  base::TaskScheduler::CreateAndStartWithDefaultParams("TakeSnapshot");
+  mojo::edk::Init();
+
+  // Take snapshot
+  gin::GinBlinkPlatform platform;
+  blink::Initialize(&platform);
+  v8::StartupData blob = blink::SnapshotCreator::TakeSnapshot();
+
+  base::FilePath file_path =
+      base::CommandLine::ForCurrentProcess()->GetSwitchValuePath("output_file");
+  CHECK(!file_path.empty());
+  base::WriteFile(file_path, blob.data, blob.raw_size);
+
+  delete[] blob.data;
+
+  return 0;
+}