Bug 1337548 - Only send DidComposite to affected tabs. r=dvander

gfx/layers/ipc/CompositorBridgeParent.cpp

@@ -1843,7 +1843,7 @@ CompositorBridgeParent::NotifyDidComposite(uint64_t aTransactionId, TimeStamp& a
 
   MonitorAutoLock lock(*sIndirectLayerTreesLock);
   ForEachIndirectLayerTree([&] (LayerTreeState* lts, const uint64_t& aLayersId) -> void {
-    if (lts->mCrossProcessParent) {
+    if (lts->mCrossProcessParent && lts->mParent == this) {
       CrossProcessCompositorBridgeParent* cpcp = lts->mCrossProcessParent;
       cpcp->DidComposite(aLayersId, aCompositeStart, aCompositeEnd);
     }