* Electron version: 1.7.5

### Expected behavior

When a theme color is no longer present the webContents did-change-theme-color event should return `null`.

### Actual behavior

The event returns `"#000000"`.

### How to reproduce

1. Log the returned color of the webContents did-change-theme-color event.
2. Go to https://electron.atom.io which has a theme color.
3. Go to https://atom.io which does not have a theme color.




atom/browser/api/atom_api_web_contents.cc
if (type_ == REMOTE)
    return;
  managed_web_contents()->CloseDevTools();
}
bool WebContents::IsDevToolsOpened() {
  if (type_ == REMOTE)
    return false;
  return managed_web_contents()->IsDevToolsViewShowing();
}
bool WebContents::IsDevToolsFocused() {
  if (type_ == REMOTE)
    return false;
  return managed_web_contents()->GetView()->IsDevToolsViewFocused();
}
void WebContents::EnableDeviceEmulation(
    const blink::WebDeviceEmulationParams& params) {
  if (type_ == REMOTE)
    return;
  Send(new ViewMsg_EnableDeviceEmulation(routing_id(), params));
}
void WebContents::DisableDeviceEmulation() {
  if (type_ == REMOTE)
    return;
  Send(new ViewMsg_DisableDeviceEmulation(routing_id()));
}
void WebContents::ToggleDevTools() {