[iOS][WK2] Rotating a zoomed PDF leads to weird scrolling behavior

[iOS][WK2] Rotating a zoomed PDF leads to weird scrolling behavior
https://bugs.webkit.org/show_bug.cgi?id=134286

Reviewed by Benjamin Poulain.

* UIProcess/ios/WKPDFView.mm:
(-[WKPDFView _computePageAndDocumentFrames]):
The WKPDFView frame and scroll view content size need to be scaled.

(-[WKPDFView web_setScrollView:]): Deleted.

(-[WKPDFView web_initWithFrame:webView:]):
Get rid of _documentFrame, and don't set it at initWithFrame: time (it's not useful yet).

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@170439 268f45cc-cd09-0410-ab3c-d52691b4dbfc