I tired with the offscreen mode and here are the problems I found:
- [x] <del>The `data` of `paint` event is empty when loading simple local pages.</del>
- [x] The size of `data` is wrong, current implement uses the size of pointer (`sizeof(bitmap_pixels)`).
- [x] Crashes when opening devtools for offscreen window.
- [x] We should probably show a dummy view indicating it is offscreen instead of provide NULL.
- [x] The offscreen window is affecting the rendering of other windows. Try running `./script/test.py -g offscreen` and then refreshing the window.

/cc @gerhardberger @brenca

atom/browser/api/atom_api_web_contents.cc
return web_contents()->GetURL();
}
base::string16 WebContents::GetTitle() const {
  return web_contents()->GetTitle();
}
bool WebContents::IsLoading() const {
  return web_contents()->IsLoading();
}
bool WebContents::IsLoadingMainFrame() const {
  
  
  return (web_contents()->GetLastCommittedURL().is_empty() ||
          web_contents()->GetSiteInstance() !=
          web_contents()->GetPendingSiteInstance()) && IsLoading();
}
bool WebContents::IsWaitingForResponse() const {
  return web_contents()->IsWaitingForResponse();
}
void WebContents::Stop() {
  web_contents()->Stop();
}
void WebContents::GoBack() {
  atom::AtomBrowserClient::SuppressRendererProcessRestartForOnce();
  web_contents()->GetController().GoBack();
}
void WebContents::GoForward() {