https://bugs.webkit.org/show_bug.cgi?id=121859
<rdar://problem/15069359>

Reviewed by Anders Carlsson.

The Mac port will now use tiled drawing for all WebKit2 views.

* Shared/DrawingAreaInfo.h:
Don't include DrawingAreaTypeImpl as a valid DrawingAreaType on Mac.

* UIProcess/API/mac/WKView.mm:
(-[WKView drawRect:]):
Remove our implementation of drawRect that paints from DrawingAreaImpl's backing store.

(-[WKView _shouldUseTiledDrawingArea]):
Removed. Always treated as if it were true, now.

(-[WKView _createDrawingAreaProxy]):
Always create a TiledCoreAnimationDrawingAreaProxy now.

(-[WKView initWithFrame:contextRef:pageGroupRef:relatedToPage:]):
(-[WKView wantsUpdateLayer]):
WKView always wants a layer, etc.

* UIProcess/BackingStore.h:
Remove Mac-specific BackingStore code, only used for DrawingAreaImpl on Mac.

* UIProcess/DrawingAreaProxy.h:
Remove an unneeded include.

* UIProcess/mac/BackingStoreMac.mm: Removed.
* WebKit2.xcodeproj/project.pbxpro...