Load the metro driver dll at startup

chrome/app/metro_driver_win.cc

+// Copyright (c) 2011 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 "metro_driver_win.h"

[darin (slow to review), 2012/03/19 16:30:45]

nit: new line above here

+
+#include <windows.h>

[darin (slow to review), 2012/03/19 16:30:45]

nit: already have this include from the header file

+
+namespace {
+// The windows 8 metro driver dll name and entry point.
+const char kMetroDriverDll[] = "metro_driver.dll";
+typedef int (*InitMetro)(LPTHREAD_START_ROUTINE thread_proc, void* context);

[darin (slow to review), 2012/03/19 16:30:45]

nit: recommend placing typedef apart from the constants

+// This environment variable controls the loading of the metro driver DLL.
+const char* kMetroModeEnvVar = "CHROME_METRO_DLL";
+
+struct Context {
+  MainFn fn;
+  HINSTANCE instance;
+};
+
+DWORD WINAPI MainThread(void* param) {
+  Context* context = reinterpret_cast<Context*>(param);
+  int rv = context->fn(context->instance);
+  delete context;
+  return rv;
+}
+
+}  // namespace
+
+MetroDriver::MetroDriver() : init_metro_fn_(NULL) {
+  if (0 != ::GetEnvironmentVariableA(kMetroModeEnvVar, NULL, 0))
+    return;
+  // We haven't tried to load the metro driver, this probably means we are the
+  // browser. Find it or not we set the environment variable because we don't
+  // want to keep trying in the child processes.
+  HMODULE metro_dll = ::LoadLibraryA(kMetroDriverDll);
+  ::SetEnvironmentVariableA(kMetroModeEnvVar, metro_dll ? "1" : "0");
+  if (!metro_dll)
+    return;
+  init_metro_fn_ =
+      ::GetProcAddress(::GetModuleHandleA(kMetroDriverDll), "InitMetro");
+}
+
+int MetroDriver::RunInMetro(HINSTANCE instance, MainFn main_fn) {
+  Context* context = new Context;
+  context->fn = main_fn;
+  context->instance = instance;
+
+  return reinterpret_cast<InitMetro>(init_metro_fn_)(&MainThread, context);
+}