Merge r185858 - ASSERT(!m_zOrderListsDirty) when mousing over web vie…

…w with incremental rendering suppressed

https://bugs.webkit.org/show_bug.cgi?id=146225

Reviewed by Zalan Bujtas.

Update RenderLayer's z-order lists when hit testing. There's no guarantee that they've
been updated; this happens to work most of the time because painting updates them,
but if incremental rendering is suppressed, we may not have painted yet.

Easy to hit on webkit.org in MiniBrowser, but I wasn't able to make a reduced testcase.

* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::hitTest):
(WebCore::RenderLayer::updateLayerListsIfNeeded): Flip the order of the tests, since checking
dirty bits is cheaper than calling isStackingContext().

Source/WebCore/ChangeLog

@@ -1,3 +1,21 @@
+2015-06-22  Simon Fraser  <simon.fraser@apple.com>
+
+        ASSERT(!m_zOrderListsDirty) when mousing over web view with incremental rendering suppressed
+        https://bugs.webkit.org/show_bug.cgi?id=146225
+
+        Reviewed by Zalan Bujtas.
+
+        Update RenderLayer's z-order lists when hit testing. There's no guarantee that they've
+        been updated; this happens to work most of the time because painting updates them,
+        but if incremental rendering is suppressed, we may not have painted yet.
+
+        Easy to hit on webkit.org in MiniBrowser, but I wasn't able to make a reduced testcase.
+
+        * rendering/RenderLayer.cpp:
+        (WebCore::RenderLayer::hitTest):
+        (WebCore::RenderLayer::updateLayerListsIfNeeded): Flip the order of the tests, since checking
+        dirty bits is cheaper than calling isStackingContext().
+
 2015-06-22  Zalan Bujtas  <zalan@apple.com>
 
         REGRESSION(r169105) Dangling renderer pointer in SelectionSubtreeRoot::SelectionSubtreeData.

Source/WebCore/rendering/RenderLayer.cpp

@@ -4777,6 +4777,8 @@ bool RenderLayer::hitTest(const HitTestRequest& request, const HitTestLocation&
 {
     ASSERT(isSelfPaintingLayer() || hasSelfPaintingLayerDescendant());
     ASSERT(!renderer().view().needsLayout());
+
+    updateLayerListsIfNeeded();
 
     LayoutRect hitTestArea = isOutOfFlowRenderFlowThread() ? downcast<RenderFlowThread>(renderer()).visualOverflowRect() : renderer().view().documentRect();
     if (!request.ignoreClipping())
@@ -6239,7 +6241,7 @@ void RenderLayer::collectLayers(bool includeHiddenLayers, CollectLayersBehavior
 
 void RenderLayer::updateLayerListsIfNeeded()
 {
-    bool shouldUpdateDescendantsAreContiguousInStackingOrder = isStackingContext() && (m_zOrderListsDirty || m_normalFlowListDirty);
+    bool shouldUpdateDescendantsAreContiguousInStackingOrder = (m_zOrderListsDirty || m_normalFlowListDirty) && isStackingContext();
     updateZOrderLists();
     updateNormalFlowList();