Add a crash-hunting CHECK() in RenderProcessHostImpl::AddRoute()

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 978916c009d46101ba764c358630c24d8b93f6eb..e44d46e796af43439074889dcc6d92847904883c 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -923,6 +923,9 @@ ServiceRegistry* RenderProcessHostImpl::GetServiceRegistry() {
 void RenderProcessHostImpl::AddRoute(
     int32 routing_id,
     IPC::Listener* listener) {
+  // We already have DCHECK() in IDMap. This is for chasing
+  // crbug.com/415059 and can be removed after fixing it.
+  CHECK(!listeners_.Lookup(routing_id));
   listeners_.AddWithID(listener, routing_id);
 }