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* Electron version: 1.7.11
* Operating system: win10 x64

i want record every frame to make a video,

### Expected behavior

stop painting page, until call startPainting()

### Actual behavior

not stop painting page

### How to reproduce
```js
const electron = require('electron');
const fs = require('fs');
const app = electron.app
const BrowserWindow = electron.BrowserWindow

let mainWindow

// app.disableHardwareAcceleration()
function createWindow() {
  mainWindow = new BrowserWindow({
    width: 480, height: 800, frame: false, resizable: false, // show: false,
    webPreferences: {
      offscreen: true
    }
  })
  // mainWindow = new BrowserWindow({ width: 480, height: 800 })
  var i = 0;
  mainWindow.webContents.on('paint', (event, dirty, image) => {
    mainWindow.webContents.stopPainting()
    const data = image.toPNG()
    fs.writeFileSync('./f/' + i++ + '.png', data)
    // mainWindow.webContents.startPainting()
  })
  mainWindow.webContents.setFrameRate(1)

  mainWindow.on('closed', function () {
    mainWindow = null
  })
  
  var url = 'https://github.com';
  mainWindow.loadURL(url)
  //mainWindow.webContents.openDevTools()

}

app.on('ready', createWindow)
app.on('window-all-closed', function () {
  if (process.platform !== 'darwin') {
    app.quit()
  }
})
app.on('activate', function () {
  if (mainWindow === null) {
    createWindow()
  }
})
```

atom/browser/api/atom_api_web_contents.cc
v8::Isolate* isolate, content::WebContents* web_contents, Type type) {
  
  return mate::CreateHandle(isolate, new WebContents(isolate, web_contents,
        type));
}
mate::Handle<WebContents> WebContents::Create(
    v8::Isolate* isolate, const mate::Dictionary& options) {
  return mate::CreateHandle(isolate, new WebContents(isolate, options));
}
}  
}  
namespace {
using atom::api::WebContents;
void Initialize(v8::Local<v8::Object> exports, v8::Local<v8::Value> unused,
                v8::Local<v8::Context> context, void* priv) {
  v8::Isolate* isolate = context->GetIsolate();
  mate::Dictionary dict(isolate, exports);
  dict.Set("WebContents", WebContents::GetConstructor(isolate)->GetFunction());
  dict.SetMethod("create", &WebContents::Create);
  dict.SetMethod("fromId", &mate::TrackableObject<WebContents>::FromWeakMapID);
  dict.SetMethod("getAllWebContents",
                 &mate::TrackableObject<WebContents>::GetAll);
}
}  
NODE_MODULE_CONTEXT_AWARE_BUILTIN(atom_browser_web_contents, Initialize)