Bug 1505363 - Call DiscardCompositorAnimations() after calling WrBridge()->EndTransaction() r=kats

Discard animations after calling WrBridge()->EndTransaction(). It updates mWrEpoch in WebRenderBridgeParent. The updated mWrEpoch is necessary for deleting animations at the correct time.

Differential Revision: https://phabricator.services.mozilla.com/D15799

gfx/layers/wr/WebRenderLayerManager.cpp

@@ -298,8 +298,6 @@ void WebRenderLayerManager::EndTransactionWithoutLayer(
     }
   }
 
-  DiscardCompositorAnimations();
-
   mWidget->AddWindowOverlayWebRenderCommands(WrBridge(), builder,
                                              resourceUpdates);
   mWindowOverlayChanged = false;
@@ -371,6 +369,11 @@ void WebRenderLayerManager::EndTransactionWithoutLayer(
                                refreshStart, mTransactionStart, mURL);
   }
 
+  // Discard animations after calling WrBridge()->EndTransaction().
+  // It updates mWrEpoch in WebRenderBridgeParent. The updated mWrEpoch is
+  // necessary for deleting animations at the correct time.
+  DiscardCompositorAnimations();
+
   mTransactionStart = TimeStamp();
 
   MakeSnapshotIfRequired(size);