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
int DevToolsWindow::GetMinimumWidth() {
  const int kMinDevToolsWidth = 150;
  return kMinDevToolsWidth;
}

int DevToolsWindow::GetMinimumWidth() {
  const int kMinDevToolsWidth = 150;
  return kMinDevToolsWidth;
}
