* Electron version: 2.0.0-beta.4
* Operating system: macOS 10.13.3

### Expected behavior

A reload of the window works.

### Actual behavior

A reload of the window does not work.

### How to reproduce

* run VSCode exploration ([download](https://az764295.vo.msecnd.net/exploration/6bc3274250cc949c7fb1d654cbb6e59c8ddad697/VSCode-darwin-exploration.zip))
* run "Reload Window" command
* sometimes I see the window stay blank after doing so and checking the console I see:

```
Uncaught (in promise) Error: Cannot get property 'id' on missing remote object 3
Error: Cannot get property 'id' on missing remote object 3
    at throwRPCError (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/browser/rpc-server.js:143:17)
    at EventEmitter.<anonymous> (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/browser/rpc-server.js:384:7)
    at emitThree (events.js:136:13)
    at EventEmitter.emit (events.js:217:7)
    at WebContents.<anonymous> (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/browser/api/web-contents.js:295:13)
    at emitTwo (events.js:126:13)
    at WebContents.emit (events.js:214:7)
    at throwRPCError (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/browser/rpc-server.js:143:17)
    at EventEmitter.<anonymous> (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/browser/rpc-server.js:384:7)
    at emitThree (events.js:136:13)
    at EventEmitter.emit (events.js:217:7)
    at WebContents.<anonymous> (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/browser/api/web-contents.js:295:13)
    at emitTwo (events.js:126:13)
    at WebContents.emit (events.js:214:7)
    at Object.exception (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/renderer/api/remote.js:209:30)
    at metaToValue (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/renderer/api/remote.js:213:28)
    at Object.descriptor.get [as id] (/Applications/Visual Studio Code - Exploration.app/Contents/Resources/electron.asar/renderer/api/remote.js:132:16)
    at file:///Applications/Visual%20Studio%20Code%20-%20Exploration.app/Contents/Resources/app/out/vs/workbench/electron-browser/bootstrap/index.js:11:97
    at new Promise (<anonymous>)
    at file:///Applications/Visual%20Studio%20Code%20-%20Exploration.app/Contents/Resources/app/out/vs/workbench/electron-browser/bootstrap/index.js:10:838
```
atom/browser/api/atom_api_web_contents.cc
const base::Callback<void(bool)>& callback) {
  auto context = GetServiceWorkerContext(web_contents());
  if (!context)
    return;
  struct WrappedCallback {
    base::Callback<void(bool)> callback_;
    explicit WrappedCallback(const base::Callback<void(bool)>& callback)
        : callback_(callback) {}
    void Run(content::ServiceWorkerCapability capability) {
      callback_.Run(capability !=
                    content::ServiceWorkerCapability::NO_SERVICE_WORKER);
      delete this;
    }
  };
  auto wrapped_callback = new WrappedCallback(callback);
  context->CheckHasServiceWorker(
      web_contents()->GetLastCommittedURL(), GURL::EmptyGURL(),
      base::Bind(&WrappedCallback::Run, base::Unretained(wrapped_callback)));
}
void WebContents::UnregisterServiceWorker(
    const base::Callback<void(bool)>& callback) {
  auto context = GetServiceWorkerContext(web_contents());
  if (!context)
    return;
  context->UnregisterServiceWorker(web_contents()->GetLastCommittedURL(),
                                   callback);
}
void WebContents::SetIgnoreMenuShortcuts(bool ignore) {