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/osr/osr_render_widget_host_view.cc
return false;
}
std::unique_ptr<content::ResizeLock>
  OffScreenRenderWidgetHostView::DelegatedFrameHostCreateResizeLock(
      bool defer_compositor_lock) {
  return nullptr;
}
void OffScreenRenderWidgetHostView::DelegatedFrameHostResizeLockWasReleased() {
  return render_widget_host_->WasResized();
}
void OffScreenRenderWidgetHostView::DelegatedFrameHostSendCompositorSwapAck(
  int output_surface_id, const cc::CompositorFrameAck& ack) {
  render_widget_host_->Send(new ViewMsg_SwapCompositorFrameAck(
    render_widget_host_->GetRoutingID(),
    output_surface_id, ack));
}
void OffScreenRenderWidgetHostView::
  DelegatedFrameHostSendReclaimCompositorResources(
    int output_surface_id, const cc::CompositorFrameAck& ack) {
  render_widget_host_->Send(new ViewMsg_ReclaimCompositorResources(
    render_widget_host_->GetRoutingID(),
    output_surface_id, ack));
}
void OffScreenRenderWidgetHostView::
  DelegatedFrameHostOnLostCompositorResources() {
  render_widget_host_->ScheduleComposite();
}
void OffScreenRenderWidgetHostView::DelegatedFrameHostUpdateVSyncParameters(