https://bugs.webkit.org/show_bug.cgi?id=111670

Patch by Tien-Ren Chen <trchen@chromium.org> on 2013-03-28
Reviewed by James Robinson.

Source/Platform:

Added WebLayerPositionConstraint for layers that need position
adjustment during threaded scrolling.
Currently it is only used for fixed-position layers.

* Platform.gypi:
* chromium/public/WebLayer.h:
(WebKit):
(WebLayer):
(WebKit::WebLayer::setPositionConstraint):
(WebKit::WebLayer::positionConstraint):
(WebKit::WebLayer::setFixedToContainerLayer):
(WebKit::WebLayer::fixedToContainerLayer):
* chromium/public/WebLayerPositionConstraint.h: Added.
(WebKit):
(WebLayerPositionConstraint):
(WebKit::WebLayerPositionConstraint::WebLayerPositionConstraint):
(WebKit::WebLayerPositionConstraint::fixedPosition):

Source/WebCore:

This patch adds support to bottom-right fixed-position elements by
introducing WebLayerPositionConstraint to WebLayer.

No new tests. Can't test until chromium patch landed.

* page/scrolling/ScrollingCoordinator.h:
(WebCore::ScrollingCoordinator::updateLayerPositionConstraint):
* page/scrolling/chromium/ScrollingCoordinatorChromium.cpp:
(WebCore::clearPositionConstraintExceptForLayer):
(WebCore):
(WebCore::computePositionConstraint):
(WebCore::ScrollingCoordinatorChromium::updateLayerPositionConstraint):
* page/scrolling/chromium/ScrollingCoordinatorChromium.h:
(ScrollingCoordinatorChromium):
* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::registerScrollingLayers):
* rendering/RenderLayerBacking.h:
(WebCore::RenderLayerBacking::contentsContainmentLayer):
(RenderLayerBacking):
* rendering/RenderLayerCompositor.cpp:
* rendering/RenderLayerCompositor.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147163 268f45cc-cd09-0410-ab3c-d52691b4dbfc