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
web_contents()->StopFinding(action);
}
void WebContents::ShowDefinitionForSelection() {
#if defined(OS_MACOSX)
  const auto view = web_contents()->GetRenderWidgetHostView();
  if (view)
    view->ShowDefinitionForSelection();
#endif
}
void WebContents::CopyImageAt(int x, int y) {
  const auto host = web_contents()->GetRenderViewHost();
  if (host)
    host->CopyImageAt(x, y);
}
void WebContents::Focus() {
  web_contents()->Focus();
}
#if !defined(OS_MACOSX)
bool WebContents::IsFocused() const {