**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
std::unique_ptr<SpellCheckClient> spell_check_client)
      : content::RenderFrameObserver(render_frame),
        spell_check_client_(std::move(spell_check_client)) {
    DCHECK(!FromRenderFrame(render_frame));
    instances_.insert(this);
  }
  ~SpellCheckerHolder() final { instances_.erase(this); }
  void UnsetAndDestroy() {
    FrameSetSpellChecker set_spell_checker(nullptr, render_frame());
    delete this;
  }
  
  void OnDestruct() final {
    
    
    
    
    
    
    
    
    
    
    delete this;
  }
  void WillReleaseScriptContext(v8::Local<v8::Context> context,