**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
blink::WebCache::ResourceTypeStats stats;
  blink::WebCache::GetResourceTypeStats(&stats);
  return stats;
}
void ClearCache(v8::Isolate* isolate) {
  isolate->IdleNotificationDeadline(0.5);
  blink::WebCache::Clear();
  base::MemoryPressureListener::NotifyMemoryPressure(
      base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL);
}
v8::Local<v8::Value> FindFrameByRoutingId(v8::Isolate* isolate,
                                          v8::Local<v8::Value> window,
                                          int routing_id) {
  content::RenderFrame* render_frame =
      content::RenderFrame::FromRoutingID(routing_id);
  if (render_frame)
    return render_frame->GetWebFrame()->MainWorldScriptContext()->Global();
  else
    return v8::Null(isolate);
}
v8::Local<v8::Value> GetOpener(v8::Isolate* isolate,