WIP android: Renders properly content outside viewports

[lucasdessy]

• When using InAppWebViewController.takeScreenshot on large contents, contents outside the viewport was not being rendered (resulted in transparent widgets). Tested on Small Phone (720x1280) APIs 25 and 28.
• This PR uses layout to pre-render the WebView before it is drawn. It also disables the scrollbars as it was being shown on the bitmap.
• It is not very well tested since this was made to fit a personal need.

Connection with issue(s)

Resolve issue #???

Connected to #???

Testing and Review Notes

Screenshots or Videos

To Do

• double check the original issue to confirm it is fully satisfied
• add testing notes and screenshots in PR description to help guide reviewers
• request the "UX" team perform a design review (if/when applicable)

[pichillilorenzo]

In the new release 6.2.0-beta.1 I added InAppWebViewController.enableSlowWholeDocumentDraw static method for Android which allows to take screenshots outside the visible viewport.
More info about it: https://pub.dev/documentation/flutter_inappwebview/6.2.0-beta.1/flutter_inappwebview/PlatformInAppWebViewController/enableSlowWholeDocumentDraw.html

So this PR shouldn't be necessary.

[lucasdessy]

Hey thanks for answering. I did use the master version, and enabling this flag didn’t change anything at all. As you can see my fork already have your implementation of InAppWebViewController.enableSlowWholeDocumentDraw on android but weirdly enough it doesn’t work. On my use, I did have to also use this method to get my draw completely done. I will try to get you more details later.