DevTools: handle devtools renderer unresponsiveness during beforeunload event interception

This patch fixes the crash which happenes under the following conditions:
1. DevTools window is in undocked state
2. DevTools renderer is unresponsive
3. User attempts to close inspected page

BUG=322380

Review URL: https://codereview.chromium.org/84883002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237611 0039d316-1c4b-4281-b951-d872f2087c98
DevToolsWindow* DevToolsWindow::OpenDevToolsWindowForWorker(
    Profile* profile,
    DevToolsAgentHost* worker_agent) {
  DevToolsWindow* window = FindDevToolsWindow(worker_agent);
  if (!window) {
    window = DevToolsWindow::CreateDevToolsWindowForWorker(profile);
    content::DevToolsManager::GetInstance()->RegisterDevToolsClientHostFor(
        worker_agent, window->frontend_host_.get());
  }
  window->Show(DevToolsToggleAction::Show());
  return window;
}

DevToolsWindow* DevToolsWindow::OpenDevToolsWindowForWorker(
    Profile* profile,
    DevToolsAgentHost* worker_agent) {
  DevToolsWindow* window = FindDevToolsWindow(worker_agent);
  if (!window) {
    window = DevToolsWindow::CreateDevToolsWindowForWorker(profile);
    content::DevToolsManager::GetInstance()->RegisterDevToolsClientHostFor(
        worker_agent, window->frontend_host_.get());
  }
  window->Show(DevToolsToggleAction::Show());
  return window;
}
