Don't coerce pointers to compositor layer mappings to booleans.

Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.cpp b/Source/core/page/scrolling/ScrollingCoordinator.cpp
index ca72786a164baa198caa2f41b0cb17abaa85f6d6..c1e947f959cef881912dbe0c08c1dcded1958ec2 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -185,14 +185,14 @@ static WebLayerPositionConstraint computePositionConstraint(const RenderLayer* l
 
         // Composited layers that inherit a fixed position state will be positioned with respect to the nearest compositedLayerMapping's GraphicsLayer.
         // So, once we find a layer that has its own compositedLayerMapping, we can stop searching for a fixed position RenderObject.
-    } while (layer && layer->compositedLayerMapping());
+    } while (layer && layer->compositingState() == PaintsIntoOwnBacking);

[shawnsingh, 2013/11/05 10:20:27]

This is not correct - see the comment immediately above.  If we don't want to
use a hasCompositedLayerMapping()  boolean, then this needs to check for both
PaintsIntoOwnBacking or HasOwnBackingButPaintsIntoAncestor.   The scenario here
is a fixed position layer that is positioned with respect to a composited
ancestor that paints into ancestor.  In that case, the fixed-pos element should
still be positioned with respect to that layer that doesn't paint anything -- it
still exists in the composited layer tree in such a way that affects positions
of its descendants.

[Ian Vollick, 2013/11/08 03:35:12]

I think the comment (and possibly the code) are wrong here. I've added comments
in the code and reverted the logic to match the current behavior until we decide
what this function should really be doing.

     return WebLayerPositionConstraint();
 }
 
 void ScrollingCoordinator::updateLayerPositionConstraint(RenderLayer* layer)
 {
     ASSERT(layer->compositedLayerMapping());
-    CompositedLayerMapping* compositedLayerMapping = layer->compositedLayerMapping();
+    CompositedLayerMappingPtr compositedLayerMapping = layer->compositedLayerMapping();
     GraphicsLayer* mainLayer = compositedLayerMapping->childForSuperlayers();
 
     // Avoid unnecessary commits
@@ -510,7 +510,7 @@ void ScrollingCoordinator::setTouchEventTargetRects(const LayerHitTestRects& lay
         WebVector<WebRect> webRects(iter->value.size());
         for (size_t i = 0; i < iter->value.size(); ++i)
             webRects[i] = enclosingIntRect(iter->value[i]);
-        CompositedLayerMapping* compositedLayerMapping = layer->compositedLayerMapping();
+        CompositedLayerMappingPtr compositedLayerMapping = layer->compositedLayerMapping();
         // If the layer is using composited scrolling, then it's the contents that these
         // rects apply to.
         GraphicsLayer* graphicsLayer = compositedLayerMapping->scrollingContentsLayer();
@@ -523,10 +523,10 @@ void ScrollingCoordinator::setTouchEventTargetRects(const LayerHitTestRects& lay
 
     // If there are any layers left that we haven't updated, clear them out.
     for (HashSet<const RenderLayer*>::iterator it = oldLayersWithTouchRects.begin(); it != oldLayersWithTouchRects.end(); ++it) {
-        if (CompositedLayerMapping* compositedLayerMapping = (*it)->compositedLayerMapping()) {
-            GraphicsLayer* graphicsLayer = compositedLayerMapping->scrollingContentsLayer();
+        if ((*it)->compositingState() == PaintsIntoOwnBacking) {

[shawnsingh, 2013/11/05 10:20:27]

I think this also needs to include HasOwnBackingButPaintsIntoAncestor... but I'm
not entirely sure.  I have a feeling there may be some existing bugs with touch
rects on composited layers that paint into ancestor already even before this
patch.

[Ian Vollick, 2013/11/08 03:35:12]

I think this is a bug, but I'm not going to fix it in this CL. I've described
the problem in a comment and changed the code to match the previous behavior.

+            GraphicsLayer* graphicsLayer = (*it)->compositedLayerMapping()->scrollingContentsLayer();
             if (!graphicsLayer)
-                graphicsLayer = compositedLayerMapping->mainGraphicsLayer();
+                graphicsLayer = (*it)->compositedLayerMapping()->mainGraphicsLayer();
             graphicsLayer->platformLayer()->setTouchEventHandlerRegion(WebVector<WebRect>());
         }
     }
@@ -553,7 +553,7 @@ void ScrollingCoordinator::touchEventTargetRectsDidChange(const Document*)
 void ScrollingCoordinator::updateScrollParentForGraphicsLayer(GraphicsLayer* child, RenderLayer* parent)
 {
     WebLayer* scrollParentWebLayer = 0;
-    if (parent && parent->compositedLayerMapping())
+    if (parent && parent->compositingState() == PaintsIntoOwnBacking)
         scrollParentWebLayer = scrollingWebLayerForGraphicsLayer(parent->compositedLayerMapping()->parentForSublayers());
 
     child->setScrollParent(scrollParentWebLayer);
@@ -562,7 +562,7 @@ void ScrollingCoordinator::updateScrollParentForGraphicsLayer(GraphicsLayer* chi
 void ScrollingCoordinator::updateClipParentForGraphicsLayer(GraphicsLayer* child, RenderLayer* parent)
 {
     WebLayer* clipParentWebLayer = 0;
-    if (parent && parent->compositedLayerMapping())
+    if (parent && parent->compositingState() == PaintsIntoOwnBacking)
         clipParentWebLayer = scrollingWebLayerForGraphicsLayer(parent->compositedLayerMapping()->parentForSublayers());
 
     child->setClipParent(clipParentWebLayer);