ServiceWorker: check if event_dispatcher is bound appropriately

R=falken@chromium.org

Bug: 817981
Change-Id: I743ee72a78c01db3d04f9d356501b14436cde9e1
Reviewed-on: https://chromium-review.googlesource.com/952586
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541371}

content/browser/service_worker/service_worker_version.h

@@ -324,7 +324,9 @@ class CONTENT_EXPORT ServiceWorkerVersion
 
   // This must be called when the worker is running.
   mojom::ServiceWorkerEventDispatcher* event_dispatcher() {
-    DCHECK(event_dispatcher_.is_bound());
+    // Temporarily CHECK for debugging https://crbug.com/817981.
+    CHECK(event_dispatcher_.is_bound());
+    CHECK(event_dispatcher_.get());
     return event_dispatcher_.get();
   }