New Webview added to view stack when coming from background

I've wrote a small app that has a webview to illustrate the issue: https://github.com/surdu/TestBkg

In the onload method of that webview I have implemented a quick mechanism to change the webview's src only the first time the onload method is called, just to illustrate better the problem.

To reproduce the problem we follow these steps:

1. launch the app on Android using tns run android. We notice the app load NS' website.
2. put the app in background by pressing the home button
3. bring back the app by pressing the app icon on the phone

On the last step is where the problem is: a new blank webview is added on top of the old one (if we press the back button on the phone, the old webview will be revealed).

Now let's consider a second scenario. After completing the above scenario, we kill the app by pressing the Overview button and close our app from there (by swipe or by pressing the X button).

Now, if we replace the step 1 by just opening the app from the phone (NOT by running tns run android) and then go through the same steps, we'll notice that at step 3 the behaviour changes: now we will be correctly presented with the old webview.

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从 app/main-page.js 中链接的复现应用开始，按照后台运行和重新打开应用的步骤，使用 tns run android 复现生命周期。跟踪应用从后台返回时 Android webview 的行为；完成标准是重新打开应用不会在现有 webview 上方添加空白 webview。