Thanks for Electron! Amazing project :)

* Electron version: 1.6.2
* Operating system: macOS Sierra (10.12.3)

It happens when `BrowserWindow` is opened with `sandbox: true`. It might be on purpose, but I couldn't find any Electron/Chromium documentation that explains why. So I'm suspecting it's a bug. I can submit a PR with a failing test to this repo if you agree that it's a bug.

### Expected behavior

`webContents`' `will-navigate` event should fire when user reloads page fx.

### Actual behavior

It does not fire.

### How to reproduce

package.json:

```json
{
  "name": "electron-sandbox-will-navigate-bug",
  "version": "0.0.0",
  "main": "main.js",
  "dependencies": {
    "electron": "^1.6.2"
  }
}
```

main.js:

```js
const {app, BrowserWindow} = require('electron')
const path = require('path')

app.on('ready', function() {
  const win = new BrowserWindow({
    webPreferences: {
      sandbox: true
    }
  })

  const {webContents} = win
  webContents.on('will-navigate', () => {
    console.log('will-navigate')
  })
  webContents.on('did-navigate', () => {
    console.log('did-navigate')
  })

  win.loadURL('file://' + path.join(__dirname, 'index.html'))
})
```

index.html:

```html
<!doctype html>
<html>
  <body>
    <button onclick="window.location.reload()">Reload</button>
  </body>
</html>
```

Perform these steps:

- Run `npm install`
- Run `./node_modules/.bin/electron .`
- Click the Reload button in the browser window
- Observe the Terminal output

Expected output:

```
did-navigate
will-navigate
did-navigate
```

Actual output:

```
did-navigate
did-navigate
```

(will-navigate is not fired).

If you outcomment the line `sandbox:true` in `main.js`, then it works as expected.
shell/browser/common_web_contents_delegate.cc
#include "components/prefs/scoped_user_pref_update.h"
#include "components/security_state/content/content_utils.h"
#include "components/security_state/core/security_state.h"
#include "content/browser/renderer_host/render_widget_host_view_base.h"  
#include "content/public/browser/browser_thread.h"
#include "content/public/browser/child_process_security_policy.h"
#include "content/public/browser/file_select_listener.h"
#include "content/public/browser/render_process_host.h"
#include "content/public/browser/render_view_host.h"
#include "content/public/browser/render_widget_host.h"
#include "content/public/browser/security_style_explanation.h"
#include "content/public/browser/security_style_explanations.h"
#include "printing/buildflags/buildflags.h"
#include "shell/browser/electron_browser_client.h"
#include "shell/browser/electron_browser_context.h"
#include "shell/browser/native_window.h"
#include "shell/browser/ui/file_dialog.h"
#include "shell/browser/web_contents_preferences.h"
#include "shell/browser/web_dialog_helper.h"
#include "shell/common/electron_constants.h"
#include "shell/common/options_switches.h"
#include "storage/browser/file_system/isolated_context.h"
#if BUILDFLAG(ENABLE_COLOR_CHOOSER)
#include "chrome/browser/ui/color_chooser.h"
#endif
#if BUILDFLAG(ENABLE_OSR)
#include "shell/browser/osr/osr_web_contents_view.h"
#endif
#if BUILDFLAG(ENABLE_PRINTING)
#include "chrome/browser/printing/print_view_manager_basic.h"