Bug 1122276 - Move lock from GetTargetNode to call sites. r=botond

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -956,13 +956,13 @@ void
 APZCTreeManager::UpdateZoomConstraints(const ScrollableLayerGuid& aGuid,
                                        const ZoomConstraints& aConstraints)
 {
+  MonitorAutoLock lock(mTreeLock);
   nsRefPtr<HitTestingTreeNode> node = GetTargetNode(aGuid, nullptr);
   MOZ_ASSERT(!node || node->GetApzc()); // any node returned must have an APZC
 
   // For a given layers id, non-root APZCs inherit the zoom constraints
   // of their root.
   if (node && node->GetApzc()->IsRootForLayersId()) {
-    MonitorAutoLock lock(mTreeLock);
     UpdateZoomConstraintsRecursively(node.get(), aConstraints);
   }
 }
@@ -1171,6 +1171,7 @@ already_AddRefed<AsyncPanZoomController>
 APZCTreeManager::GetTargetAPZC(const ScrollableLayerGuid& aGuid,
                                GuidComparator aComparator)
 {
+  MonitorAutoLock lock(mTreeLock);
   nsRefPtr<HitTestingTreeNode> node = GetTargetNode(aGuid, aComparator);
   MOZ_ASSERT(!node || node->GetApzc()); // any node returned must have an APZC
   nsRefPtr<AsyncPanZoomController> apzc = node ? node->GetApzc() : nullptr;
@@ -1181,7 +1182,7 @@ already_AddRefed<HitTestingTreeNode>
 APZCTreeManager::GetTargetNode(const ScrollableLayerGuid& aGuid,
                                GuidComparator aComparator)
 {
-  MonitorAutoLock lock(mTreeLock);
+  mTreeLock.AssertCurrentThreadOwns();
   nsRefPtr<HitTestingTreeNode> target = FindTargetNode(mRootNode, aGuid, aComparator);
   return target.forget();
 }