Add a basic Mojo app that initializes V8

mojo/apps/js/main.cc

+// Copyright 2013 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 "mojo/apps/js/v8_environment.h"
+#include "mojo/public/system/core.h"
+#include "mojo/public/system/macros.h"
+
+#if defined(WIN32)
+#if !defined(CDECL)
+#define CDECL __cdecl
+#endif
+#define MOJO_APPS_JS_EXPORT __declspec(dllexport)
+#else
+#define CDECL
+#define MOJO_APPS_JS_EXPORT __attribute__((visibility("default")))
+#endif
+
+extern "C" MOJO_APPS_JS_EXPORT MojoResult CDECL MojoMain(
+    mojo::Handle pipe) {
+  mojo::apps::InitializeV8();
+  // TODO(abarth): Load JS off the network and execute it.
+  return MOJO_RESULT_OK;
+}