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
content::NavigationHandle* navigation_handle) {
  bool is_main_frame = navigation_handle->IsInMainFrame();
  if (navigation_handle->HasCommitted() && !navigation_handle->IsErrorPage()) {
    auto url = navigation_handle->GetURL();
    bool is_in_page = navigation_handle->IsSamePage();
    if (is_main_frame && !is_in_page) {
      Emit("did-navigate", url);
    } else if (is_in_page) {
      Emit("did-navigate-in-page", url);
    }
  } else {
    auto url = navigation_handle->GetURL();
    int code = navigation_handle->GetNetErrorCode();
    auto description = net::ErrorToShortString(code);
    Emit("did-fail-provisional-load", code, description, url, is_main_frame);
    
    if (code != net::ERR_ABORTED)
      Emit("did-fail-load", code, description, url, is_main_frame);
  }
}
void WebContents::TitleWasSet(content::NavigationEntry* entry,