iOS broken after r165342
https://bugs.webkit.org/show_bug.cgi?id=129987

Reviewed by Simon Fraser.

* NetworkProcess/ios/NetworkProcessIOS.mm:
(WebKit::NetworkProcess::platformLowMemoryHandler): Add missing stub implementation for
platformLowMemoryHandler().

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@165347 268f45cc-cd09-0410-ab3c-d52691b4dbfc
[iOS] Don't call scrollOffsetForFixedPosition a second time if we have no header and footer layers
https://bugs.webkit.org/show_bug.cgi?id=129912

Reviewed by Tim Horton.

Avoid extra work if we have no header or footer layers.

* page/scrolling/ios/ScrollingTreeScrollingNodeIOS.mm:
(WebCore::ScrollingTreeScrollingNodeIOS::setScrollLayerPosition):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@165348 268f45cc-cd09-0410-ab3c-d52691b4dbfc
[iOS WK2] Get position:fixed working slighlty better
https://bugs.webkit.org/show_bug.cgi?id=129988

Source/WebCore:

Reviewed by Dan Bernstein.

On iOS we want to use the viewport-constrained visible rect, not
just the visible rect.

* page/scrolling/AsyncScrollingCoordinator.cpp:
(WebCore::AsyncScrollingCoordinator::frameViewLayoutUpdated):

Source/WebKit2:

Reviewed by Dan Bernstein.

iOS uses fixed layout, but does not want fixed elements laid
out relative to the frame.

* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::setUseFixedLayout):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@165349 268f45cc-cd09-0410-ab3c-d52691b4dbfc