* Output of `node_modules/.bin/electron --version`: v3.0.5
* Operating System (Platform and Version): macOS 10.14

**Expected Behavior**
When webPreferences.sandbox is set to true and webFrame is using a provider for spell checking, the memory must be released after page reload.

**Actual behavior**
The memory isn't released and caused memory leak

**To Reproduce**

- Clone https://github.com/vrbsm/example-memory-leak-electron
- Run npm run start
Memory usage of electron process will be increasing in task manager after reloading the page several times

**Screenshots**
![test-memory-leak-01](https://user-images.githubusercontent.com/9887288/47675838-c2d4b800-db99-11e8-97e8-b5b27bcab929.gif)



atom/renderer/api/atom_api_web_frame.cc
v8::Local<v8::Context> context =
      v8::Local<v8::Object>::Cast(value)->CreationContext();
  if (context.IsEmpty())
    return nullptr;
  blink::WebLocalFrame* frame = blink::WebLocalFrame::FrameForContext(context);
  if (!frame)
    return nullptr;
  return content::RenderFrame::FromWebFrame(frame);
}
class RenderFrameStatus : public content::RenderFrameObserver {