Bug 1122276 - Inline the BuildOverscrollHandoffChain callsite of GetTargetAPZC to avoid re-entering the tree lock and deadlocking. r=botond

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -1168,11 +1168,10 @@ APZCTreeManager::HitTestAPZC(const ScreenIntPoint& aPoint)
 }
 
 already_AddRefed<AsyncPanZoomController>
-APZCTreeManager::GetTargetAPZC(const ScrollableLayerGuid& aGuid,
-                               GuidComparator aComparator)
+APZCTreeManager::GetTargetAPZC(const ScrollableLayerGuid& aGuid)
 {
   MonitorAutoLock lock(mTreeLock);
-  nsRefPtr<HitTestingTreeNode> node = GetTargetNode(aGuid, aComparator);
+  nsRefPtr<HitTestingTreeNode> node = GetTargetNode(aGuid, nullptr);
   MOZ_ASSERT(!node || node->GetApzc()); // any node returned must have an APZC
   nsRefPtr<AsyncPanZoomController> apzc = node ? node->GetApzc() : nullptr;
   return apzc.forget();
@@ -1263,8 +1262,9 @@ APZCTreeManager::BuildOverscrollHandoffChain(const nsRefPtr<AsyncPanZoomControll
     }
     if (!scrollParent) {
       ScrollableLayerGuid guid(parent->GetGuid().mLayersId, 0, apzc->GetScrollHandoffParentId());
-      nsRefPtr<AsyncPanZoomController> scrollParentPtr = GetTargetAPZC(guid, &GuidComparatorIgnoringPresShell);
-      scrollParent = scrollParentPtr.get();
+      nsRefPtr<HitTestingTreeNode> node = GetTargetNode(guid, &GuidComparatorIgnoringPresShell);
+      MOZ_ASSERT(!node || node->GetApzc()); // any node returned must have an APZC
+      scrollParent = node ? node->GetApzc() : nullptr;
     }
     apzc = scrollParent;
   }

gfx/layers/apz/src/APZCTreeManager.h

@@ -413,8 +413,7 @@ private:
   void AttachNodeToTree(HitTestingTreeNode* aNode,
                         HitTestingTreeNode* aParent,
                         HitTestingTreeNode* aNextSibling);
-  already_AddRefed<AsyncPanZoomController> GetTargetAPZC(const ScrollableLayerGuid& aGuid,
-                                                         GuidComparator aComparator = nullptr);
+  already_AddRefed<AsyncPanZoomController> GetTargetAPZC(const ScrollableLayerGuid& aGuid);
   already_AddRefed<HitTestingTreeNode> GetTargetNode(const ScrollableLayerGuid& aGuid,
                                                      GuidComparator aComparator);
   HitTestingTreeNode* FindTargetNode(HitTestingTreeNode* aNode,