* 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
Emit("will-destroy");
  ResetManagedWebContents(async);
}
bool WebContents::DidAddMessageToConsole(content::WebContents* source,
                                         int32_t level,
                                         const base::string16& message,
                                         int32_t line_no,
                                         const base::string16& source_id) {
  if (type_ == BROWSER_WINDOW || type_ == OFF_SCREEN) {
    return false;
  } else {
    Emit("console-message", level, message, line_no, source_id);
    return true;
  }
}
void WebContents::OnCreateWindow(
    const GURL& target_url,
    const std::string& frame_name,
    WindowOpenDisposition disposition,
    const std::vector<std::string>& features,
    const scoped_refptr<content::ResourceRequestBodyImpl>& body) {
  if (type_ == BROWSER_WINDOW || type_ == OFF_SCREEN)
    Emit("-new-window", target_url, frame_name, disposition, features, body);
  else
    Emit("new-window", target_url, frame_name, disposition, features);
}
void WebContents::WebContentsCreated(content::WebContents* source_contents,