Define our own Node entry

Chromium's V8 is using external startup snapshot file while Node does
not, so we have to use Chromium's gin for V8 initialization.

atom/app/node_main.cc

@@ -0,0 +1,56 @@
+// Copyright (c) 2015 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "atom/app/node_main.h"
+
+#include "atom/browser/javascript_environment.h"
+#include "atom/common/node_includes.h"
+#include "gin/array_buffer.h"
+#include "gin/public/isolate_holder.h"
+
+namespace atom {
+
+int NodeMain(int argc, char *argv[]) {
+  argv = uv_setup_args(argc, argv);
+  int exec_argc;
+  const char** exec_argv;
+  node::Init(&argc, const_cast<const char**>(argv), &exec_argc, &exec_argv);
+
+  int exit_code = 1;
+  {
+    gin::IsolateHolder::LoadV8Snapshot();
+    gin::IsolateHolder::Initialize(
+        gin::IsolateHolder::kNonStrictMode,
+        gin::ArrayBufferAllocator::SharedInstance());
+
+    JavascriptEnvironment gin_env;
+    node::Environment* env = node::CreateEnvironment(
+        gin_env.isolate(), gin_env.context(), argc, argv, exec_argc, exec_argv);
+
+    bool more;
+    do {
+      more = uv_run(env->event_loop(), UV_RUN_ONCE);
+      if (more == false) {
+        node::EmitBeforeExit(env);
+
+        // Emit `beforeExit` if the loop became alive either after emitting
+        // event, or after running some callbacks.
+        more = uv_loop_alive(env->event_loop());
+        if (uv_run(env->event_loop(), UV_RUN_NOWAIT) != 0)
+          more = true;
+      }
+    } while (more == true);
+
+    exit_code = node::EmitExit(env);
+    node::RunAtExit(env);
+
+    env->Dispose();
+  }
+
+  v8::V8::Dispose();
+
+  return exit_code;
+}
+
+}  // namespace atom