--- a/gfx/layers/wr/WebRenderLayerManager.cpp
+++ b/gfx/layers/wr/WebRenderLayerManager.cpp
@@ -565,16 +565,22 @@ WebRenderLayerManager::SetTransactionIdA
     if (aAllocator) {
       aAllocator->ResetInitialTransactionId(mTransactionIdAllocator->LastTransactionId());
     }
   }
 
   mTransactionIdAllocator = aAllocator;
 }
 
+TransactionId
+WebRenderLayerManager::GetLastTransactionId()
+{
+  return mLatestTransactionId;
+}
+
 void
 WebRenderLayerManager::AddDidCompositeObserver(DidCompositeObserver* aObserver)
 {
   if (!mDidCompositeObservers.Contains(aObserver)) {
     mDidCompositeObservers.AppendElement(aObserver);
   }
 }
 

--- a/gfx/layers/wr/WebRenderLayerManager.h
+++ b/gfx/layers/wr/WebRenderLayerManager.h
@@ -97,16 +97,17 @@ public:
                             const mozilla::TimeStamp& aCompositeStart,
                             const mozilla::TimeStamp& aCompositeEnd) override;
 
   virtual void ClearCachedResources(Layer* aSubtree = nullptr) override;
   virtual void UpdateTextureFactoryIdentifier(const TextureFactoryIdentifier& aNewIdentifier) override;
   virtual TextureFactoryIdentifier GetTextureFactoryIdentifier() override;
 
   virtual void SetTransactionIdAllocator(TransactionIdAllocator* aAllocator) override;
+  virtual TransactionId GetLastTransactionId() override;
 
   virtual void AddDidCompositeObserver(DidCompositeObserver* aObserver) override;
   virtual void RemoveDidCompositeObserver(DidCompositeObserver* aObserver) override;
 
   virtual void FlushRendering() override;
   virtual void WaitOnTransactionProcessed() override;
 
   virtual void SendInvalidRegion(const nsIntRegion& aRegion) override;