Flash of garbage pixels when playing a show on Hulu

<https://webkit.org/b/119871>

Source/WebCore:

Reviewed by Tim Horton.

When starting a show on Hulu, there's a layer that gets marked as
opaque because it has a child RenderLayer whose background fills the
compositing layer. That child RenderLayer was recently position:fixed
but outside the viewport, so its viewportConstrainedNotCompositedReason
was set to a non-zero value.

However, we failed to clear the viewportConstrainedNotCompositedReason
when the layer became non-fixed. This caused painting the opaque
layer to bail in RenderLayer::paintLayer(), leaving garbage.

Test: compositing/contents-opaque/fixed-to-nonfixed.html

* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::paintLayer): Add an assertion to catch this error in future.
* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::updateBacking): Make sure we clear the
ViewportConstrainedNotCompositedReason if the layer is no longer fixed.

Change-Id: Ie1aa935b8271cd8cc3159f5337d483a77d74b8a0
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154147 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Michael Bruning <michael.bruning@digia.com>

0 files changed, 0 insertions, 0 deletions