* 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
#include "atom/renderer/api/atom_api_web_frame.h"
#include <utility>
#include "atom/common/api/api_messages.h"
#include "atom/common/api/event_emitter_caller.h"
#include "atom/common/native_mate_converters/blink_converter.h"
#include "atom/common/native_mate_converters/callback.h"
#include "atom/common/native_mate_converters/gfx_converter.h"
#include "atom/common/native_mate_converters/string16_converter.h"
#include "atom/renderer/api/atom_api_spell_check_client.h"
#include "base/memory/memory_pressure_listener.h"
#include "content/public/renderer/render_frame.h"
#include "content/public/renderer/render_frame_observer.h"
#include "content/public/renderer/render_frame_visitor.h"
#include "content/public/renderer/render_view.h"
#include "native_mate/dictionary.h"
#include "native_mate/object_template_builder.h"
#include "third_party/blink/public/platform/web_cache.h"
#include "third_party/blink/public/web/web_custom_element.h"
#include "third_party/blink/public/web/web_document.h"
#include "third_party/blink/public/web/web_element.h"
#include "third_party/blink/public/web/web_frame_widget.h"
#include "third_party/blink/public/web/web_ime_text_span.h"
#include "third_party/blink/public/web/web_input_method_controller.h"
#include "third_party/blink/public/web/web_local_frame.h"
#include "third_party/blink/public/web/web_script_execution_callback.h"