Use a boolean hasCompositedLayerMapping() accessor instead of the pointer

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..60f66e39bdbba63b7496fa358fdcaf575b4e5237 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -172,7 +172,7 @@ static void clearPositionConstraintExceptForLayer(GraphicsLayer* layer, Graphics
 
 static WebLayerPositionConstraint computePositionConstraint(const RenderLayer* layer)
 {
-    ASSERT(layer->compositedLayerMapping());
+    ASSERT(layer->hasCompositedLayerMapping());
     do {
         if (layer->renderer()->style()->position() == FixedPosition) {
             const RenderObject* fixedPositionObject = layer->renderer();
@@ -185,13 +185,13 @@ 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->hasCompositedLayerMapping());
     return WebLayerPositionConstraint();
 }
 
 void ScrollingCoordinator::updateLayerPositionConstraint(RenderLayer* layer)
 {
-    ASSERT(layer->compositedLayerMapping());
+    ASSERT(layer->hasCompositedLayerMapping());
     CompositedLayerMapping* compositedLayerMapping = layer->compositedLayerMapping();
     GraphicsLayer* mainLayer = compositedLayerMapping->childForSuperlayers();
 
@@ -523,7 +523,8 @@ 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()) {
+        if ((*it)->hasCompositedLayerMapping()) {
+            CompositedLayerMapping* compositedLayerMapping = (*it)->compositedLayerMapping();
             GraphicsLayer* graphicsLayer = compositedLayerMapping->scrollingContentsLayer();
             if (!graphicsLayer)
                 graphicsLayer = compositedLayerMapping->mainGraphicsLayer();
@@ -553,7 +554,7 @@ void ScrollingCoordinator::touchEventTargetRectsDidChange(const Document*)
 void ScrollingCoordinator::updateScrollParentForGraphicsLayer(GraphicsLayer* child, RenderLayer* parent)
 {
     WebLayer* scrollParentWebLayer = 0;
-    if (parent && parent->compositedLayerMapping())
+    if (parent && parent->hasCompositedLayerMapping())
         scrollParentWebLayer = scrollingWebLayerForGraphicsLayer(parent->compositedLayerMapping()->parentForSublayers());
 
     child->setScrollParent(scrollParentWebLayer);
@@ -562,7 +563,7 @@ void ScrollingCoordinator::updateScrollParentForGraphicsLayer(GraphicsLayer* chi
 void ScrollingCoordinator::updateClipParentForGraphicsLayer(GraphicsLayer* child, RenderLayer* parent)
 {
     WebLayer* clipParentWebLayer = 0;
-    if (parent && parent->compositedLayerMapping())
+    if (parent && parent->hasCompositedLayerMapping())
         clipParentWebLayer = scrollingWebLayerForGraphicsLayer(parent->compositedLayerMapping()->parentForSublayers());
 
     child->setClipParent(clipParentWebLayer);