Bug 1465162 - don't crash in ContentParent::RecvDeallocateLayerTreeId if the content parent ID doesn't exist; r=jld

MozReview-Commit-ID: IyLyhVUsOow

--HG--
extra : rebase_source : 5537174ddbc12cc56a17f0b8eca44501fb35d83c

dom/ipc/ContentParent.cpp

@@ -1624,7 +1624,7 @@ ContentParent::RecvDeallocateLayerTreeId(const ContentParentId& aCpId,
 
   ContentProcessManager* cpm = ContentProcessManager::GetSingleton();
   RefPtr<ContentParent> contentParent = cpm->GetContentProcessById(aCpId);
-  if (!contentParent->CanCommunicateWith(ChildID())) {
+  if (!contentParent || !contentParent->CanCommunicateWith(ChildID())) {
     return IPC_FAIL(this, "Spoofed DeallocateLayerTreeId call");
   }