* 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
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() {
  atom::AtomBrowserClient::SuppressRendererProcessRestartForOnce();
  web_contents()->GetController().GoForward();
}
void WebContents::GoToOffset(int offset) {