Remove wrong DCHECK in ServiceWorkerContextWatcher::OnControlleeAdded

It turns out that it's not always true that the new controllee is not
already in the clients map. This CL removes the DCHECK introduced in
https://chromium-review.googlesource.com/c/chromium/src/+/2151246 and
restores the initial behavior. base::InsertOrAssign() is used instead
of the former usage of the square bracket operator so that a default
constructor for ServiceWorkerClientInfo is not needed.

Bug: 1077372
Change-Id: I4ae7270cc8e757cb0b7662d5d41a7ea0ce3d1f4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2176287Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Patrick Monette <pmonette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#766474}

content/browser/service_worker/service_worker_context_watcher.cc

@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/bind.h"
+#include "base/stl_util.h"
 #include "base/task/post_task.h"
 #include "content/browser/service_worker/embedded_worker_status.h"
 #include "content/browser/service_worker/service_worker_context_wrapper.h"
@@ -348,8 +349,7 @@ void ServiceWorkerContextWatcher::OnControlleeAdded(
     return;
   ServiceWorkerVersionInfo* version = it->second.get();
 
-  bool inserted = version->clients.emplace(uuid, info).second;
-  DCHECK(inserted);
+  base::InsertOrAssign(version->clients, uuid, info);
 
   SendVersionInfo(*version);
 }