[webview_flutter]Adding error message display on iOS WebView

[hatzyuta]

On iOS, when WebView failed to load web pages for some reasons(e.g. 'ATS' on iOS),there is no process to show error messages to developers in the current version of 'webview_flutter' plugin.
I added error message display especially on iOS so that developers realize the reason why webview fails to load.

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[hatzyuta]

I signed it!

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CLAs look good, thanks!

[ened]

Could this also happen on Android?

[hatzyuta]

@ened
'ATS' is specific to iOS,but Android's webview often fails to load due to mis-setting(e.g. permission).
Should I add the same code on Android ,too?

[ened]

@hatzyuta Perhaps yes, especially as the INTERNET permission on Android is not per se a requirement for WebView. (It could be used to display a bundled HTML file, too). I think it would be good to have complete error logs on all platforms.

[hatzyuta]

@ened
OK, I will. Thanks.

[hatzyuta]

@ened
I also added the same code on Android.

[ened]

@hatzyuta lovely. @amirh is this something for you?

[amirh]

Thanks for the contribution! left a comment, this will also need to be rebased.

[amirh]

I'd suggest that we allow the Flutter application to register error listeners and invoke these, giving the app developer the power to decide whether to print error messages or to do something else with them.

[amirh]

It actually seems that what I've suggested is addressed by #1788 given that the other PR is closer to be merge-able I'd suggest closing the current PR.

[amirh]

Closing this PR as the issue is addressed by #1788