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::AsDevToolsWindow(
    content::RenderViewHost* window_rvh) {
  if (g_instances == NULL)
    return NULL;
  DevToolsWindows* instances = &g_instances.Get();
  for (DevToolsWindows::iterator it(instances->begin()); it != instances->end();
       ++it) {
    if ((*it)->web_contents_->GetRenderViewHost() == window_rvh)
      return *it;
  }
  return NULL;
}

DevToolsWindow* DevToolsWindow::AsDevToolsWindow(
    content::RenderViewHost* window_rvh) {
  if (g_instances == NULL)
    return NULL;
  DevToolsWindows* instances = &g_instances.Get();
  for (DevToolsWindows::iterator it(instances->begin()); it != instances->end();
       ++it) {
    if ((*it)->web_contents_->GetRenderViewHost() == window_rvh)
      return *it;
  }
  return NULL;
}
