**Is your feature request related to a problem? Please describe.**
After webContents.insertCSS() I cant find a way to remove injected stylesheet.

**Describe the solution you'd like**
insert: webContents.insertCSS('style-id', 'body { ... }') or .inserCSS('body { ... })'
remove: webContents.removeCSS('style-id') or .removeCSS() to remove all injected stylesheets


atom/renderer/api/atom_api_web_frame.cc
args->GetNext(&scriptExecutionType);
  
  
  
  GetRenderFrame(window)->GetWebFrame()->RequestExecuteScriptInIsolatedWorld(
      world_id, &sources.front(), sources.size(), has_user_gesture,
      scriptExecutionType, new ScriptExecutionCallback(std::move(promise)));
  return handle;
}
void SetIsolatedWorldInfo(v8::Local<v8::Value> window,
                          int world_id,
                          const mate::Dictionary& options,
                          mate::Arguments* args) {
  std::string origin_url, security_policy, name;
  options.Get("securityOrigin", &origin_url);
  options.Get("csp", &security_policy);
  options.Get("name", &name);
  if (!security_policy.empty() && origin_url.empty()) {
    args->ThrowError(
        "If csp is specified, securityOrigin should also be specified");
    return;
  }
  blink::WebIsolatedWorldInfo info;
  info.security_origin = blink::WebSecurityOrigin::CreateFromString(
      blink::WebString::FromUTF8(origin_url));
  info.content_security_policy = blink::WebString::FromUTF8(security_policy);
  info.human_readable_name = blink::WebString::FromUTF8(name);
  GetRenderFrame(window)->GetWebFrame()->SetIsolatedWorldInfo(world_id, info);
}
blink::WebCache::ResourceTypeStats GetResourceUsage(v8::Isolate* isolate) {