Add a minimalistic SPI to control the layout size outside of WKView

https://bugs.webkit.org/show_bug.cgi?id=127403

Patch by Benjamin Poulain <bpoulain@apple.com> on 2014-01-22
Reviewed by Sam Weinig.

The API lets a client of WKView force the layout size. Once the size
is set this way, default update is disabled and the client needs to
update the size systematically as needed. This is done to avoid double
layout or flickering.

* UIProcess/API/Cocoa/WKViewPrivate.h:
* UIProcess/API/ios/WKViewIOS.mm:
(-[WKView _frameOrBoundsChanged]):
(-[WKView overrideMinimumLayoutSize:]):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162590 268f45cc-cd09-0410-ab3c-d52691b4dbfc