https://bugs.webkit.org/show_bug.cgi?id=127373

Reviewed by Beth Dakin.

Instead of PLATFORM(IOS) #idefs at every call site for viewportConstrainedVisibleContentRect(),
move the #ifdef inside viewportConstrainedVisibleContentRect().

The one call site that needs special handling is RenderLayerBacking::updateCompositedBounds(),
which needs to avoid clipping fixed layers to the custom fixed position rect, but instead to
visibleContentRect() (which is really the document bounds on iOS). This ensures that the
fixed layers aren't clipped when zooming out.

* page/FrameView.cpp:
(WebCore::FrameView::viewportConstrainedVisibleContentRect):
* rendering/RenderBoxModelObject.cpp:
(WebCore::RenderBoxModelObject::stickyPositionOffset):
* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::updateCompositedBounds):
* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::requiresCompositingForPosition):
(WebCore::RenderLayerCompositor::computeFixedViewportConstraints):
(WebCore::RenderLayerCompositor::computeStickyViewportConstraints):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162480 268f45cc-cd09-0410-ab3c-d52691b4dbfc