Add private interface to WKView to asynchronously update the drawing area size
https://bugs.webkit.org/show_bug.cgi?id=114549

Reviewed by Simon Fraser.

This will allow a client using the WKView to resize the contents without blocking waiting for the web process to repaint.

* UIProcess/API/mac/WKView.mm:
(-[WKView _setDrawingAreaSize:]):
    - if the new size of teh drawing area does not match the frame size, position it according to the contentAnchor.
(-[WKView updateLayer]):
    - Don't let a subsequent frame size change block on a prior async resize.
(-[WKView forceAsyncDrawingAreaSizeUpdate:]):
    - resize the drawing area asynchronously, even if frame size udpates are disabled.
(-[WKView waitForAsyncDrawingAreaSizeUpdate]):
    - wait for asynchronous updates to complete.

* UIProcess/API/mac/WKViewPrivate.h:
    - declare new methods.

* UIProcess/DrawingAreaProxy.cpp:
(WebKit):
* UIProcess/DrawingAreaProxy.h:
(DrawingAreaProxy):
(WebKit::DrawingAreaProxy::waitForPossibleGeometryUpdate):
* UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.h:
(TiledCoreAnimationDrawingAreaProxy):
* UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.mm:
(WebKit::TiledCoreAnimationDrawingAreaProxy::waitForPossibleGeometryUpdate):
    - pass timeout for waitForPossibleGeometryUpdate as a parameter.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148331 268f45cc-cd09-0410-ab3c-d52691b4dbfc