mus: Fix creating the factory for window-tree-client in renderer.

content/renderer/mus/renderer_window_tree_client.cc

Index: content/renderer/mus/renderer_window_tree_client.cc
diff --git a/content/renderer/mus/renderer_window_tree_client.cc b/content/renderer/mus/renderer_window_tree_client.cc
index e9827f8c0a65c1fb216981f8c307d6157039e48c..a6dec993ae3d51329ca331ce18f0c3283a5dea85 100644
--- a/content/renderer/mus/renderer_window_tree_client.cc
+++ b/content/renderer/mus/renderer_window_tree_client.cc
@@ -26,9 +26,9 @@ RendererWindowTreeClient* RendererWindowTreeClient::Get(int routing_id) {
 }
 
 // static
-void RendererWindowTreeClient::Create(int routing_id) {
-  DCHECK(g_connections.Get().find(routing_id) == g_connections.Get().end())
-      << routing_id;
+void RendererWindowTreeClient::CreateIfNecessary(int routing_id) {
+  if (Get(routing_id))
+    return;
   RendererWindowTreeClient* connection =
       new RendererWindowTreeClient(routing_id);
   g_connections.Get().insert(std::make_pair(routing_id, connection));