Bug 1539306 - Use the current producer/frame id for mask layers, since they never set the previous one. r=mstange

Depends on D25302

Differential Revision: https://phabricator.services.mozilla.com/D25303

--HG--
extra : moz-landing-system : lando

gfx/layers/LayerTreeInvalidation.cpp

@@ -624,8 +624,16 @@ struct ImageLayerProperties : public LayerPropertiesBase {
         mLastFrameID(-1),
         mIsMask(aIsMask) {
     if (mImageHost) {
-      mLastProducerID = mImageHost->GetLastProducerID();
-      mLastFrameID = mImageHost->GetLastFrameID();
+      if (aIsMask) {
+        // Mask layers never set the 'last' producer/frame
+        // id, since they never get composited as their own
+        // layer.
+        mLastProducerID = mImageHost->GetProducerID();
+        mLastFrameID = mImageHost->GetFrameID();
+      } else {
+        mLastProducerID = mImageHost->GetLastProducerID();
+        mLastFrameID = mImageHost->GetLastFrameID();
+      }
     }
   }